<PAGE>   1
      As filed with the Securities and Exchange Commission on March 12, 2001
                                                   Registration No. 333-________
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549

                     ---------------------------------------

                                    FORM S-8
                        REGISTRATION STATEMENT UNDER THE
                             SECURITIES ACT OF 1933

                         United Therapeutics Corporation
            --------------------------------------------------------
             (Exact Name of Registrant as Specified in Its Charter)

      DELAWARE                                               52-1984749
---------------------                                ---------------------------
(State or Other Jurisdiction                               (IRS Employer
of Incorporation)                                        Identification No.)

                               1110 Spring Street
                             Silver Spring, MD 20910
                                 (301) 608-9292
                  --------------------------------------------
                    (Address of Principal Executive Offices,
                               Including Zip Code)

          Employee Options Granted Outside the Equity Incentive Plan on
                                 March 24, 1997
          Employee Options Granted Outside the Equity Incentive Plan on
                                 April 30, 1997
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 June 26, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                               September 4, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 30, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 March 15, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 March 20, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                 April 14, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                  May 1, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                  May 26, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                 July 10, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                               September 4, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                               September 6, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 4, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                October 26, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 30, 2000
  Employee and Consultant Options Granted Outside the Equity Incentive Plan on
                               December 14, 2000
  ----------------------------------------------------------------------------
                            (Full Title of the Plans)


<PAGE>   2


           Martine A. Rothblatt, Chairman and Chief Executive Officer
                         United Therapeutics Corporation
                               1110 Spring Street
                             Silver Spring, MD 20910
                                 (301) 608-9292
                  --------------------------------------------
            (Name, Address, Including Zip Code, and Telephone Number,
                   Including Area Code, of Agent For Service)

                        Copies of all correspondence to:

                               LaDawn Naegle, Esq.
                                 Bryan Cave LLP
                         700 13th Street, NW, Suite 700
                            Washington, DC 20005-3960
                                 (202) 508-6000




<PAGE>   3


                         CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
---------------------------------------------------------------------------------------------------------------------
          Title of Each                                       Proposed              Proposed             Amount
       Class of Securities                Amount               Maximum              Maximum                of
              To Be                        To Be           Offering Price          Aggregate          Registration
            Registered                 Registered(1)         Per Unit(2)         Offering Price           Fee
---------------------------------------------------------------------------------------------------------------------
<S>                                            <C>                   <C>               <C>                <C>
Common Stock, par value
$.01 per share (3)                                1,666                $3.00             $4,998.00             $1.25

Common Stock, par value
$.01 per share (3)                                  833                $3.00             $2,499.00             $0.63

Common Stock, par value
$.01 per share (3)                                1,666               $18.00            $29,988.00             $7.50

Common Stock, par value
$.01 per share (3)                                1,667               $27.50            $45,842.50            $11.47

Common Stock, par value
$.01 per share (3)                                5,001              $30.120           $150,630.22            $37.67

Common Stock, par value
$.01 per share (3)                                1,667               $68.25           $113,772.75            $28.45

Common Stock, par value
$.01 per share (3)                                6,666               $57.13           $380,828.58            $95.21

Common Stock, par value
$.01 per share (3)                              207,000               $41.56         $8,602,920.00         $2,150.73

Common Stock, par value
$.01 per share (3)                              100,000               $65.06         $6,506,000.00         $1,626.50

Common Stock, par value
$.01 per share (3)                               20,000               $62.25         $1,245,000.00           $311.25

Common Stock, par value
$.01 per share (3)                                3,900              $116.38           $453,822.00           $113.46

Common Stock, par value
$.01 per share (3)                                1,667               $86.50           $144,195.50            $36.05

Common Stock, par value
$.01 per share (3)                                2,500               $46.00           $115,000.00            $28.75

Common Stock, par value
$.01 per share (3)                                4,000              $77.125              $308,500            $77.13

Common Stock, par value
$.01 per share (3)                                9,600               $51.81           $497,376.00           $124.35

Common Stock, par value
$.01 per share (3)                                5,001              $49.938           $249,739.94            $62.44

Common Stock, par value
$.01 per share (3)                              673,000               $14.48            $9,745,040         $2,436.26

---------------------------------------------------------------------------------------------------------------------
Total fee                                                                                                  $7,149.10
</TABLE>


<PAGE>   4


(1)  Represents (i) 1,666 shares of Common Stock issuable upon exercise of
     options granted to an employee on March 24, 1997, (ii) 833 shares of common
     stock issuable upon exercise of options granted to an employee on April 30,
     1997, (iii) 1,666 shares of Common Stock issuable upon exercise of options
     granted to a consultant on June 26, 1999, (iv) 1,667 shares of common stock
     issuable upon exercise of options granted to a consultant on September 4,
     1999, (v) 5,001 shares of Common Stock issuable upon exercise of options
     granted to consultants on October 30, 1999, (vi) 1,667 shares of common
     stock issuable upon exercise of options granted to a consultant on March
     15, 2000, (vii) 6,666 shares of common stock issuable upon exercise of
     options granted to consultants on March 20, 2000, (viii) 207,000 shares of
     common stock issuable upon exercise of options granted to employees on
     April 14, 2000, (ix) 100,000 shares of common stock issuable upon exercise
     of options granted to an employee on May 1, 2000, (x) 20,000 shares of
     common stock issuable upon exercise of options granted to an employee on
     May 26, 2000, (xi) 3,900 shares of common stock issuable upon exercise of
     options granted to an employee on July 10, 2000, (xii) 1,667 shares of
     common stock issuable upon exercise of options granted to a consultant on
     September 4, 2000, (xiii) 2,500 shares of common stock issuable upon
     exercise of options granted to an employee on September 6, 2000, (xiv)
     4,000 shares of common stock issuable upon exercise of options granted to a
     consultant on October 4, 2000, (xv) 9,600 shares of common stock issuable
     upon exercise of options granted to employees on October 26, 2000, (xvi)
     5,001 shares of common stock issuable upon exercise of options granted to
     consultants on October 30, 2000, and (xvii) 673,000 shares of common stock
     issuable upon exercise of options granted to employees and consultants on
     December 14, 2000.

(2)  Calculated solely for the purpose of determining the registration fee
     pursuant to Rule 457(h), based on the actual exercise prices of outstanding
     options issued pursuant to the plans.

(3)  Includes associated preferred stock purchase rights.


<PAGE>   5


                                     PART I
                           INFORMATION REQUIRED IN THE
                            SECTION 10(a) PROSPECTUS


Item 1.  Plan Information.

         Information required by Part I of Form S-8 to be contained in the
Section 10(a) prospectus is omitted from this registration statement in
accordance with Rule 428 under the Securities Act of 1933, as amended
("Securities Act"), and the Note to Part I of Form S-8.

Item 2.  Registrant Information and Employee Plan Annual Information.

         Information required by Part I of Form S-8 to be contained in the
Section 10(a) prospectus is omitted from this registration statement in
accordance with Rule 428 under the Securities Act and the Note to Part I of Form
S-8.



<PAGE>   6


                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


Item 3.  Incorporation of Documents by Reference.

        The following documents, which previously have been filed by United
Therapeutics Corporation (the "Company") with the Securities and Exchange
Commission (the "Commission"), are incorporated herein by reference and made a
part hereof:

        (1) Annual Report on Form 10-K for the fiscal year ended December 31,
            1999, filed with the Commission on March 22, 2000 (File No.
            0-26301).

        (2) Quarterly Reports on Form 10-Q for the quarters ended March 31,
            2000, June 30, 2000 and September 30, 2000.

        (3) Current Reports on Form 8-K dated January 18, 2000, June 27, 2000,
            June 29, 2000, July 13, 2000, December 1, 2000, December 5, 2000,
            December 7, 2000, December 17, 2000, December 18, 2000 (as amended)
            and December 29, 2000 (as amended).

        (4) The description of the Company's Common Stock contained in
            Post-Effective Amendment No. 1 to Registration Statement on Form S-1
            (Registration No. 333-76409), filed June 17, 1999, and Registration
            Statement on Form 8-A (Registration No. 333-76409), filed June 8,
            1999, as amended on January 2, 2001, including any amendment filed
            for the purposes of updating such description.

        All documents filed by the Company with the Commission pursuant to
Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date
hereof shall hereby be deemed to be incorporated by reference in this
Registration Statement and to be a part hereof from the date of filing of such
documents.

        Any statement contained in a document incorporated or deemed to be
incorporated herein by reference shall be deemed to be modified or superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in any other subsequently filed document incorporated or
deemed to be incorporated herein by reference modifies or supersedes such
statement. Any statement contained herein shall be deemed to be modified or
superseded for purposes of this Registration Statement to the extent that a
statement contained in any subsequently filed document incorporated or deemed to
be incorporated herein by reference modifies or supersedes such statement. Any
such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.





                                      II-1
<PAGE>   7

Item 4.  Description of Securities.

         Not applicable.

Item 5.  Interests of Named Experts and Counsel.

         None.

Item 6.  Indemnification of Directors and Officers.

         As permitted by Delaware law, the Company's Amended and Restated
Certificate of Incorporation provides that no director of the Company will be
personally liable to the Company or its stockholders for monetary damages for
breach of fiduciary duty as a director, except for liability (a) for any breach
of duty of loyalty to United Therapeutics or to its stockholders, (b) for acts
or omissions not in good faith or that involve intentional misconduct or a
knowing violation of law, (c) under Section 174 of the Delaware General
Corporation Law, or (d) for any transaction from which the director derived an
improper personal benefit.

         The Company's Amended and Restated Certificate of Incorporation further
provides that the Company must indemnify its directors and executive officers
and may indemnify its other officers and employees and agents to the fullest
extent permitted by Delaware law. The Company believes that indemnification
under its Amended and Restated Certificate of Incorporation covers negligence
and gross negligence on the part of indemnified parties.

         The Company has entered into indemnification agreements with each of
its directors and officers. These agreements, among other things, require the
Company to indemnify such directors and officers for certain expenses (including
attorneys' fees), judgments, fines and settlement amounts incurred by any such
person in any action or proceeding, including any action by or in the right of
the Company, arising out of such person's services as a director or officer of
the Company, any subsidiary of the Company or any other company or enterprise to
which the person provides services at the request of the Company.

Item 7.  Exemption from Registration Claimed.

                  Not applicable.

Item 8.  Exhibits.

         No.      Description
         ---      -----------

         4.1      Reference is made to the Amended and Restated Certificate of
                  Incorporation of the Registrant, incorporated by reference to
                  Exhibit 3.1 of the Registrant's Registration Statement on Form
                  S-1 (Registration No. 333-76409), and the Amended and Restated
                  By-Laws of the Registrant, incorporated by reference to



                                      II-2
<PAGE>   8

                  Exhibit 3.2 of the Registrant's Registration Statement on Form
                  S-1 (Registration No. 333-76409).

         5        Opinion of Bryan Cave LLP

         23.1     Consent of KPMG LLP

         23.2     Consent of Bryan Cave LLP (included in Exhibit 5 hereto)

         24       Power of Attorney (included on signature page)





                                      II-3
<PAGE>   9



Item 9.  Undertakings.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
Section 10 (a)(3) of the Securities Act;

                           (ii)     To reflect in the prospectus any facts or
events arising after the effective date of the Registration Statement (or the
most recent post-effective amendment thereof) which, individually or in the
aggregate, represent a fundamental change in the information set forth in the
Registration Statement. Notwithstanding the foregoing, any increase or decrease
in volume of securities offered (if the total dollar value of securities offered
would not exceed that which was registered) and any deviation from the low or
high end of the estimated maximum offering range may be reflected in the form of
prospectus filed with the Commission pursuant to Rule 424(b) if, in the
aggregate, the changes in volume and price represent no more than a 20 percent
change in the maximum aggregate offering price set forth in the "Calculation of
Registration Fee" table in the effective registration statement;

                           (iii)    To include any material information with
respect to the plan of distribution not previously disclosed in this
Registration Statement or any material change to such information in this
Registration Statement.

                  (2)      That, for the purpose of determining any liability
under the Securities Act of 1933, each such post-effective amendment shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

                  (3)      To remove from registration by means of a
post-effective amendment any of the securities being registered which remain
unsold at the termination of the offering.

         (b)      The undersigned Registrant hereby undertakes that, for the
purposes of determining any liability under the Securities Act of 1933, each
filing of the Registrant's annual report pursuant to Section 13(a) or 15(d) of
the Securities Exchange Act of 1934 that is incorporated by reference in the
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and that the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

         (c)      Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions or otherwise, the
Registrant has been advised that in the opinion of the



                                      II-4
<PAGE>   10

Securities and Exchange Commission such indemnification is against public policy
as expressed in the Act and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question of whether
such indemnification by it is against public policy as expressed in the Act and
will be governed by the final adjudication of such issue.





                                      II-5
<PAGE>   11



                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Silver Spring, State of Maryland, on January 3,
2001.

                         UNITED THERAPEUTICS CORPORATION


                         By:  /s/ Martine A. Rothblatt
                              ------------------------
                              Martine A. Rothblatt
                              Chairman of the Board and Chief Executive Officer

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement has been signed below by the following persons in
the capacities and on the dates indicated. Each of such persons appoints Martine
A. Rothblatt, and Paul A. Mahon, or either of them, with full power to act, his
true and lawful attorney-in-fact and agent of him and on his behalf and in his
name, place and stead, and in any and all capacities, with full and several
power of substitution, to sign and file with the proper authorities any and all
documents in connection with this Registration Statement on Form S-8, granting
unto said attorney, full power and authority to do and perform each and every
act and thing requisite and necessary to be done in and about the premises in
order to effectuate the same as fully to all intents and purposes as he might or
could do if personally present, hereby ratifying and confirming all that said
attorney-in-fact and agent, may lawfully do or cause to be done by virtue
hereof.

<TABLE>
<CAPTION>
          Signature                                          Title                                   Date

<S>                                      <C>                                                    <C>
/s/ Martine A. Rothblatt                 Chairman of the Board and Chief Executive Officer      January 3, 2001
------------------------
Martine A. Rothblatt

/s/ James W. Crow                        President, Chief Operating Officer and Director        January 3, 2001
-----------------
James W. Crow

/s/ Fred T. Hadeed                       Chief Financial Officer                                January 3, 2001
------------------
Fred T. Hadeed

/s/ Gilles Cloutier                      Executive Vice President, Treasurer and Director       January 3, 2001
-------------------
Gilles Cloutier
</TABLE>



                                      II-6
<PAGE>   12

<TABLE>
<CAPTION>
          Signature                                          Title                                   Date

<S>                                      <C>                                                    <C>
/s/ Shelmer D. Blackburn, Jr.            Vice President of Operations, Secretary and Director   January 3, 2001
-----------------------------
Shelmer D. Blackburn, Jr.

/s/ Noah A. Samara                       Director                                               January 3, 2001
------------------
Noah A. Samara

/s/ David Gooray                         Director                                               January 3, 2001
----------------
David Gooray

/s/ Wayne Roe                            Director                                               January 3, 2001
-------------
Wayne Roe

/s/ H. Beecher Hicks                     Director                                               January 3, 2001
-------------------
H. Beecher Hicks

/s/ Michael C. Miles                     Director                                               January 3, 2001
-------------------
Michael C. Miles

/s/ John Cooke                           Director                                               January 3, 2001
--------------
John Cooke
</TABLE>



                                      II-7
[{"type": "S-8", "sequence": "1", "filename": "w44842s-8.txt", "description": "FORM S-8", "secsgml_size_bytes": 24525}]
{"company-data": {"conformed-name": "UNITED THERAPEUTICS CORP", "cik": "0001082554", "assigned-sic": "2834", "irs-number": "521984749", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-56922", "film-number": "1566759"}, "business-address": {"street1": "1110 SPRING ST", "city": "SILVER SPRING", "state": "MD", "zip": "20910", "phone": "3016089292"}, "mail-address": {"street1": "1110 SPRING ST", "city": "SILVER SPRING", "state": "MD", "zip": "20910"}}
1
      As filed with the Securities and Exchange Commission on March 12, 2001
                                                   Registration No. 333-________
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549

                     ---------------------------------------

                                    FORM S-8
                        REGISTRATION STATEMENT UNDER THE
                             SECURITIES ACT OF 1933

                         United Therapeutics Corporation
            --------------------------------------------------------
             (Exact Name of Registrant as Specified in Its Charter)

      DELAWARE                                               52-1984749
---------------------                                ---------------------------
(State or Other Jurisdiction                               (IRS Employer
of Incorporation)                                        Identification No.)

                               1110 Spring Street
                             Silver Spring, MD 20910
                                 (301) 608-9292
                  --------------------------------------------
                    (Address of Principal Executive Offices,
                               Including Zip Code)

          Employee Options Granted Outside the Equity Incentive Plan on
                                 March 24, 1997
          Employee Options Granted Outside the Equity Incentive Plan on
                                 April 30, 1997
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 June 26, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                               September 4, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 30, 1999
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 March 15, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                 March 20, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                 April 14, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                  May 1, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                  May 26, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                 July 10, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                               September 4, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                               September 6, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 4, 2000
          Employee Options Granted Outside the Equity Incentive Plan on
                                October 26, 2000
         Consultant Options Granted Outside the Equity Incentive Plan on
                                October 30, 2000
  Employee and Consultant Options Granted Outside the Equity Incentive Plan on
                               December 14, 2000
  ----------------------------------------------------------------------------
                            (Full Title of the Plans)
2

           Martine A. Rothblatt, Chairman and Chief Executive Officer
                         United Therapeutics Corporation
                               1110 Spring Street
                             Silver Spring, MD 20910
                                 (301) 608-9292
                  --------------------------------------------
            (Name, Address, Including Zip Code, and Telephone Number,
                   Including Area Code, of Agent For Service)

                        Copies of all correspondence to:

                               LaDawn Naegle, Esq.
                                 Bryan Cave LLP
                         700 13th Street, NW, Suite 700
                            Washington, DC 20005-3960
                                 (202) 508-6000
3

                         CALCULATION OF REGISTRATION FEE
---------------------------------------------------------------------------------------------------------------------
          Title of Each                                       Proposed              Proposed             Amount
       Class of Securities                Amount               Maximum              Maximum                of
              To Be                        To Be           Offering Price          Aggregate          Registration
            Registered                 Registered(1)         Per Unit(2)         Offering Price           Fee
---------------------------------------------------------------------------------------------------------------------
Common Stock, par value
$.01 per share (3)                                1,666                $3.00             $4,998.00             $1.25

Common Stock, par value
$.01 per share (3)                                  833                $3.00             $2,499.00             $0.63

Common Stock, par value
$.01 per share (3)                                1,666               $18.00            $29,988.00             $7.50

Common Stock, par value
$.01 per share (3)                                1,667               $27.50            $45,842.50            $11.47

Common Stock, par value
$.01 per share (3)                                5,001              $30.120           $150,630.22            $37.67

Common Stock, par value
$.01 per share (3)                                1,667               $68.25           $113,772.75            $28.45

Common Stock, par value
$.01 per share (3)                                6,666               $57.13           $380,828.58            $95.21

Common Stock, par value
$.01 per share (3)                              207,000               $41.56         $8,602,920.00         $2,150.73

Common Stock, par value
$.01 per share (3)                              100,000               $65.06         $6,506,000.00         $1,626.50

Common Stock, par value
$.01 per share (3)                               20,000               $62.25         $1,245,000.00           $311.25

Common Stock, par value
$.01 per share (3)                                3,900              $116.38           $453,822.00           $113.46

Common Stock, par value
$.01 per share (3)                                1,667               $86.50           $144,195.50            $36.05

Common Stock, par value
$.01 per share (3)                                2,500               $46.00           $115,000.00            $28.75

Common Stock, par value
$.01 per share (3)                                4,000              $77.125              $308,500            $77.13

Common Stock, par value
$.01 per share (3)                                9,600               $51.81           $497,376.00           $124.35

Common Stock, par value
$.01 per share (3)                                5,001              $49.938           $249,739.94            $62.44

Common Stock, par value
$.01 per share (3)                              673,000               $14.48            $9,745,040         $2,436.26

---------------------------------------------------------------------------------------------------------------------
Total fee                                                                                                  $7,149.10
4

(1)  Represents (i) 1,666 shares of Common Stock issuable upon exercise of
     options granted to an employee on March 24, 1997, (ii) 833 shares of common
     stock issuable upon exercise of options granted to an employee on April 30,
     1997, (iii) 1,666 shares of Common Stock issuable upon exercise of options
     granted to a consultant on June 26, 1999, (iv) 1,667 shares of common stock
     issuable upon exercise of options granted to a consultant on September 4,
     1999, (v) 5,001 shares of Common Stock issuable upon exercise of options
     granted to consultants on October 30, 1999, (vi) 1,667 shares of common
     stock issuable upon exercise of options granted to a consultant on March
     15, 2000, (vii) 6,666 shares of common stock issuable upon exercise of
     options granted to consultants on March 20, 2000, (viii) 207,000 shares of
     common stock issuable upon exercise of options granted to employees on
     April 14, 2000, (ix) 100,000 shares of common stock issuable upon exercise
     of options granted to an employee on May 1, 2000, (x) 20,000 shares of
     common stock issuable upon exercise of options granted to an employee on
     May 26, 2000, (xi) 3,900 shares of common stock issuable upon exercise of
     options granted to an employee on July 10, 2000, (xii) 1,667 shares of
     common stock issuable upon exercise of options granted to a consultant on
     September 4, 2000, (xiii) 2,500 shares of common stock issuable upon
     exercise of options granted to an employee on September 6, 2000, (xiv)
     4,000 shares of common stock issuable upon exercise of options granted to a
     consultant on October 4, 2000, (xv) 9,600 shares of common stock issuable
     upon exercise of options granted to employees on October 26, 2000, (xvi)
     5,001 shares of common stock issuable upon exercise of options granted to
     consultants on October 30, 2000, and (xvii) 673,000 shares of common stock
     issuable upon exercise of options granted to employees and consultants on
     December 14, 2000.

(2)  Calculated solely for the purpose of determining the registration fee
     pursuant to Rule 457(h), based on the actual exercise prices of outstanding
     options issued pursuant to the plans.

(3)  Includes associated preferred stock purchase rights.
5

                                     PART I
                           INFORMATION REQUIRED IN THE
                            SECTION 10(a) PROSPECTUS

Item 1.  Plan Information.

         Information required by Part I of Form S-8 to be contained in the
Section 10(a) prospectus is omitted from this registration statement in
accordance with Rule 428 under the Securities Act of 1933, as amended
("Securities Act"), and the Note to Part I of Form S-8.

Item 2.  Registrant Information and Employee Plan Annual Information.

         Information required by Part I of Form S-8 to be contained in the
Section 10(a) prospectus is omitted from this registration statement in
accordance with Rule 428 under the Securities Act and the Note to Part I of Form
S-8.
6

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

Item 3.  Incorporation of Documents by Reference.

        The following documents, which previously have been filed by United
Therapeutics Corporation (the "Company") with the Securities and Exchange
Commission (the "Commission"), are incorporated herein by reference and made a
part hereof:

        (1) Annual Report on Form 10-K for the fiscal year ended December 31,
            1999, filed with the Commission on March 22, 2000 (File No.
            0-26301).

        (2) Quarterly Reports on Form 10-Q for the quarters ended March 31,
            2000, June 30, 2000 and September 30, 2000.

        (3) Current Reports on Form 8-K dated January 18, 2000, June 27, 2000,
            June 29, 2000, July 13, 2000, December 1, 2000, December 5, 2000,
            December 7, 2000, December 17, 2000, December 18, 2000 (as amended)
            and December 29, 2000 (as amended).

        (4) The description of the Company's Common Stock contained in
            Post-Effective Amendment No. 1 to Registration Statement on Form S-1
            (Registration No. 333-76409), filed June 17, 1999, and Registration
            Statement on Form 8-A (Registration No. 333-76409), filed June 8,
            1999, as amended on January 2, 2001, including any amendment filed
            for the purposes of updating such description.

        All documents filed by the Company with the Commission pursuant to
Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act subsequent to the date
hereof shall hereby be deemed to be incorporated by reference in this
Registration Statement and to be a part hereof from the date of filing of such
documents.

        Any statement contained in a document incorporated or deemed to be
incorporated herein by reference shall be deemed to be modified or superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in any other subsequently filed document incorporated or
deemed to be incorporated herein by reference modifies or supersedes such
statement. Any statement contained herein shall be deemed to be modified or
superseded for purposes of this Registration Statement to the extent that a
statement contained in any subsequently filed document incorporated or deemed to
be incorporated herein by reference modifies or supersedes such statement. Any
such statement so modified or superseded shall not be deemed, except as so
modified or superseded, to constitute a part of this Registration Statement.

                                      II-1
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Item 4.  Description of Securities.

         Not applicable.

Item 5.  Interests of Named Experts and Counsel.

         None.

Item 6.  Indemnification of Directors and Officers.

         As permitted by Delaware law, the Company's Amended and Restated
Certificate of Incorporation provides that no director of the Company will be
personally liable to the Company or its stockholders for monetary damages for
breach of fiduciary duty as a director, except for liability (a) for any breach
of duty of loyalty to United Therapeutics or to its stockholders, (b) for acts
or omissions not in good faith or that involve intentional misconduct or a
knowing violation of law, (c) under Section 174 of the Delaware General
Corporation Law, or (d) for any transaction from which the director derived an
improper personal benefit.

         The Company's Amended and Restated Certificate of Incorporation further
provides that the Company must indemnify its directors and executive officers
and may indemnify its other officers and employees and agents to the fullest
extent permitted by Delaware law. The Company believes that indemnification
under its Amended and Restated Certificate of Incorporation covers negligence
and gross negligence on the part of indemnified parties.

         The Company has entered into indemnification agreements with each of
its directors and officers. These agreements, among other things, require the
Company to indemnify such directors and officers for certain expenses (including
attorneys' fees), judgments, fines and settlement amounts incurred by any such
person in any action or proceeding, including any action by or in the right of
the Company, arising out of such person's services as a director or officer of
the Company, any subsidiary of the Company or any other company or enterprise to
which the person provides services at the request of the Company.

Item 7.  Exemption from Registration Claimed.

                  Not applicable.

Item 8.  Exhibits.

         No.      Description
         ---      -----------

         4.1      Reference is made to the Amended and Restated Certificate of
                  Incorporation of the Registrant, incorporated by reference to
                  Exhibit 3.1 of the Registrant's Registration Statement on Form
                  S-1 (Registration No. 333-76409), and the Amended and Restated
                  By-Laws of the Registrant, incorporated by reference to

                                      II-2
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                  Exhibit 3.2 of the Registrant's Registration Statement on Form
                  S-1 (Registration No. 333-76409).

         5        Opinion of Bryan Cave LLP

         23.1     Consent of KPMG LLP

         23.2     Consent of Bryan Cave LLP (included in Exhibit 5 hereto)

         24       Power of Attorney (included on signature page)

                                      II-3
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Item 9.  Undertakings.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
Section 10 (a)(3) of the Securities Act;

                           (ii)     To reflect in the prospectus any facts or
events arising after the effective date of the Registration Statement (or the
most recent post-effective amendment thereof) which, individually or in the
aggregate, represent a fundamental change in the information set forth in the
Registration Statement. Notwithstanding the foregoing, any increase or decrease
in volume of securities offered (if the total dollar value of securities offered
would not exceed that which was registered) and any deviation from the low or
high end of the estimated maximum offering range may be reflected in the form of
prospectus filed with the Commission pursuant to Rule 424(b) if, in the
aggregate, the changes in volume and price represent no more than a 20 percent
change in the maximum aggregate offering price set forth in the "Calculation of
Registration Fee" table in the effective registration statement;

                           (iii)    To include any material information with
respect to the plan of distribution not previously disclosed in this
Registration Statement or any material change to such information in this
Registration Statement.

                  (2)      That, for the purpose of determining any liability
under the Securities Act of 1933, each such post-effective amendment shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

                  (3)      To remove from registration by means of a
post-effective amendment any of the securities being registered which remain
unsold at the termination of the offering.

         (b)      The undersigned Registrant hereby undertakes that, for the
purposes of determining any liability under the Securities Act of 1933, each
filing of the Registrant's annual report pursuant to Section 13(a) or 15(d) of
the Securities Exchange Act of 1934 that is incorporated by reference in the
Registration Statement shall be deemed to be a new registration statement
relating to the securities offered therein, and that the offering of such
securities at that time shall be deemed to be the initial bona fide offering
thereof.

         (c)      Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions or otherwise, the
Registrant has been advised that in the opinion of the

                                      II-4
10

Securities and Exchange Commission such indemnification is against public policy
as expressed in the Act and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such director, officer or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question of whether
such indemnification by it is against public policy as expressed in the Act and
will be governed by the final adjudication of such issue.

                                      II-5
11

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, as amended,
the Registrant certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Silver Spring, State of Maryland, on January 3,
2001.

                         UNITED THERAPEUTICS CORPORATION

                         By:  /s/ Martine A. Rothblatt
                              ------------------------
                              Martine A. Rothblatt
                              Chairman of the Board and Chief Executive Officer

         Pursuant to the requirements of the Securities Act of 1933, as amended,
this registration statement has been signed below by the following persons in
the capacities and on the dates indicated. Each of such persons appoints Martine
A. Rothblatt, and Paul A. Mahon, or either of them, with full power to act, his
true and lawful attorney-in-fact and agent of him and on his behalf and in his
name, place and stead, and in any and all capacities, with full and several
power of substitution, to sign and file with the proper authorities any and all
documents in connection with this Registration Statement on Form S-8, granting
unto said attorney, full power and authority to do and perform each and every
act and thing requisite and necessary to be done in and about the premises in
order to effectuate the same as fully to all intents and purposes as he might or
could do if personally present, hereby ratifying and confirming all that said
attorney-in-fact and agent, may lawfully do or cause to be done by virtue
hereof.
Signature                                          Title                                   Date
/s/ Martine A. Rothblatt                 Chairman of the Board and Chief Executive Officer      January 3, 2001
------------------------
Martine A. Rothblatt

/s/ James W. Crow                        President, Chief Operating Officer and Director        January 3, 2001
-----------------
James W. Crow

/s/ Fred T. Hadeed                       Chief Financial Officer                                January 3, 2001
------------------
Fred T. Hadeed

/s/ Gilles Cloutier                      Executive Vice President, Treasurer and Director       January 3, 2001
-------------------
Gilles Cloutier
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Signature                                          Title                                   Date
/s/ Shelmer D. Blackburn, Jr.            Vice President of Operations, Secretary and Director   January 3, 2001
-----------------------------
Shelmer D. Blackburn, Jr.

/s/ Noah A. Samara                       Director                                               January 3, 2001
------------------
Noah A. Samara

/s/ David Gooray                         Director                                               January 3, 2001
----------------
David Gooray

/s/ Wayne Roe                            Director                                               January 3, 2001
-------------
Wayne Roe

/s/ H. Beecher Hicks                     Director                                               January 3, 2001
-------------------
H. Beecher Hicks

/s/ Michael C. Miles                     Director                                               January 3, 2001
-------------------
Michael C. Miles

/s/ John Cooke                           Director                                               January 3, 2001
--------------
John Cooke
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