<PAGE>   1
    As filed with the Securities and Exchange Commission on January 26, 2000
                                                   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)

                   Amended and Restated Equity Incentive Plan
                       (As Amended Through June 11, 1999)
                                       and
                      Employee Non-Qualified Stock Options
                   -------------------------------------------
                            (Full Title of the Plans)

           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>   2




                         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        Offering Price           Fee
--------------------- --------------------- ---------------- -------------------- ---------------
<S>                     <C>                 <C>              <C>                  <C>
Common Stock, par
value $.01 per share       13,733,373            75.09(2)      $1,031,238,979.00    $272,247.09

Common Stock par
value $.01 per share        1,306,144                 (3)          20,879,141.00       5,512.09
-------------------------------------------------------------------------------------------------
Total fee                                                                           $277,759.18
</TABLE>

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

(1) Includes such additional indeterminate number of shares as may be issuable
    pursuant to the anti-dilution provisions of the Plans. Includes 13,590,526
    shares issuable pursuant to the Amended and Restated Equity Incentive Plan,
    1,348,991 shares subject to options issued pursuant to the Plan and 100,000
    shares issuable pursuant to an agreement between the Registrant and an
    employee.

(2) Estimated solely for the purposes of determining the registration fee
    pursuant to Rule 457(c), based upon the average of the closing bid and ask
    prices for the Common Stock on January 19, 2000, as reported by the Nasdaq
    National Market.

(3) Calculated solely for the purpose of determining the registration fee
    pursuant to Rule 457(h), based on the actual exercise prices of currently
    outstanding options issued pursuant to the plan covering 1,306,144 shares.
<PAGE>   3


                                     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>   4


                                     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)  424(b) Prospectus relating to Registration Statement on Form S-1
              (Registration No. 333-93853), dated January 18, 2000.

         (2)  Quarterly Reports on Form 10-Q for the periods ended June 30, 1999
              and September 30, 1999.

         (3)  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, 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.

Item 4.  Description of Securities.

        Not applicable.

                                      II-1
<PAGE>   5

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

                                      II-2
<PAGE>   6

        4.2    Registration Rights Agreement, dated as of October 30, 1998, by
               and among the Registrant, Merrill Lynch KECALP L.P. 1997, and
               Merrill Lynch KECALP International L.P. 1997, incorporated by
               reference to Exhibit 4.2 of the Registrant's Registration
               Statement on Form S-1 (Registration No. 333-76409).

        4.3    Form of Common Stock Purchase Agreement, executed as of March
               1998, by and between the Registrant and each of Community
               Investment Partners III L.P., LLLP, Mary Ellen and Raul Evelio
               Perez, Trustees of the Mary Ellen Perez revocable trust dated
               October 28, 1993, Edward D. Jones & Co., Oakwood Investors I,
               L.L.C. and James L. Nouss, Jr., incorporated by reference to
               Exhibit 4.3 of the Registrant's Registration Statement on form
               S-1 (Registration No. 333-76409).

        4.4    Warrant to purchase shares of United Therapeutics common stock,
               issued on November 2, 1998 to Cortech, Inc., incorporated by
               reference to Exhibit 4.4 of the Registrant's Registration
               Statement on form S-1 (Registration No. 333-76409).


        4.5    Stock Option Grant to purchase shares of United Therapeutics'
               common stock, issued on September 16, 1998, to Toray Industries,
               Inc., incorporated by reference to Exhibit 4.5 of the
               Registrant's Registration Statement on form S-1 (Registration No.
               333-76409).

        4.6    Registration Rights Agreement, dated as of October 7, 1999, by
               and among the Registrant and Robert M. Moriarty, Ph.D., Raju
               Penmasta, Ph.D., Lian Guo, Ph.D., George W. Davis, Esq. and David
               Moriarty, incorporated by reference to Exhibit 10.2 of the
               Registrant's Form 10-Q for the period ended September 30, 1999.

        4.7    Form of Purchase Agreement dated as of December 22, 1999,
               incorporated by reference to Exhibit 4.7 of the Registrant's
               Registration Statement on Form S-1 (Registration No. 333-93853).

        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>   7



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>   8

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>   9


                                   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 24,
2000.

                                    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 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 the
Registration Statement on Form S-8, filed with the Securities and Exchange
Commission on January 26, 2000, 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 24, 2000
Martine A. Rothblatt

/s/ James W. Crow                     President, Chief Operating Officer and
-----------------------------         Director                                 January 24, 2000
James W. Crow


/s/ Gilles Cloutier                   Chief Financial Officer, Chief
-----------------------------         Accounting Officer, Executive Vice
Gilles Cloutier                       President, Treasurer and Director        January 24, 2000
</TABLE>



                                      II-6
<PAGE>   10

<TABLE>
<CAPTION>
       SIGNATURE                                 TITLE                              DATE
<S>                                   <C>                                      <C>
/s/ Shelmer D. Blackburn, Jr.         Vice President of Operations,
-----------------------------         Secretary and Director                   January 24, 2000
Shelmer D. Blackburn, Jr.

/s/ Jean Guy-Lambert                  Director                                 January 24, 2000
-----------------------------
Jean Guy-Lambert

/s/ Noah A. Samara                    Director                                 January 24, 2000
-----------------------------
Noah A. Samara

/s/ David Gooray                      Director                                 January 24, 2000
-----------------------------
David Gooray

/s/ Olivia Giscard d'Estaing          Director                                 January 24, 2000
-----------------------------
Olivia Giscard d'Estaing
</TABLE>

                                      II-7
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 20370}]
{"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": "333-95419", "film-number": "513618"}, "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 January 26, 2000
                                                   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)

                   Amended and Restated Equity Incentive Plan
                       (As Amended Through June 11, 1999)
                                       and
                      Employee Non-Qualified Stock Options
                   -------------------------------------------
                            (Full Title of the Plans)

           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
2

                         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        Offering Price           Fee
--------------------- --------------------- ---------------- -------------------- ---------------
Common Stock, par
value $.01 per share       13,733,373            75.09(2)      $1,031,238,979.00    $272,247.09

Common Stock par
value $.01 per share        1,306,144                 (3)          20,879,141.00       5,512.09
-------------------------------------------------------------------------------------------------
Total fee                                                                           $277,759.18
--------------------------------------------------------------------------------

(1) Includes such additional indeterminate number of shares as may be issuable
    pursuant to the anti-dilution provisions of the Plans. Includes 13,590,526
    shares issuable pursuant to the Amended and Restated Equity Incentive Plan,
    1,348,991 shares subject to options issued pursuant to the Plan and 100,000
    shares issuable pursuant to an agreement between the Registrant and an
    employee.

(2) Estimated solely for the purposes of determining the registration fee
    pursuant to Rule 457(c), based upon the average of the closing bid and ask
    prices for the Common Stock on January 19, 2000, as reported by the Nasdaq
    National Market.

(3) Calculated solely for the purpose of determining the registration fee
    pursuant to Rule 457(h), based on the actual exercise prices of currently
    outstanding options issued pursuant to the plan covering 1,306,144 shares.
3

                                     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.
4

                                     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)  424(b) Prospectus relating to Registration Statement on Form S-1
              (Registration No. 333-93853), dated January 18, 2000.

         (2)  Quarterly Reports on Form 10-Q for the periods ended June 30, 1999
              and September 30, 1999.

         (3)  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, 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.

Item 4.  Description of Securities.

        Not applicable.

                                      II-1
5

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

                                      II-2
6

        4.2    Registration Rights Agreement, dated as of October 30, 1998, by
               and among the Registrant, Merrill Lynch KECALP L.P. 1997, and
               Merrill Lynch KECALP International L.P. 1997, incorporated by
               reference to Exhibit 4.2 of the Registrant's Registration
               Statement on Form S-1 (Registration No. 333-76409).

        4.3    Form of Common Stock Purchase Agreement, executed as of March
               1998, by and between the Registrant and each of Community
               Investment Partners III L.P., LLLP, Mary Ellen and Raul Evelio
               Perez, Trustees of the Mary Ellen Perez revocable trust dated
               October 28, 1993, Edward D. Jones & Co., Oakwood Investors I,
               L.L.C. and James L. Nouss, Jr., incorporated by reference to
               Exhibit 4.3 of the Registrant's Registration Statement on form
               S-1 (Registration No. 333-76409).

        4.4    Warrant to purchase shares of United Therapeutics common stock,
               issued on November 2, 1998 to Cortech, Inc., incorporated by
               reference to Exhibit 4.4 of the Registrant's Registration
               Statement on form S-1 (Registration No. 333-76409).

        4.5    Stock Option Grant to purchase shares of United Therapeutics'
               common stock, issued on September 16, 1998, to Toray Industries,
               Inc., incorporated by reference to Exhibit 4.5 of the
               Registrant's Registration Statement on form S-1 (Registration No.
               333-76409).

        4.6    Registration Rights Agreement, dated as of October 7, 1999, by
               and among the Registrant and Robert M. Moriarty, Ph.D., Raju
               Penmasta, Ph.D., Lian Guo, Ph.D., George W. Davis, Esq. and David
               Moriarty, incorporated by reference to Exhibit 10.2 of the
               Registrant's Form 10-Q for the period ended September 30, 1999.

        4.7    Form of Purchase Agreement dated as of December 22, 1999,
               incorporated by reference to Exhibit 4.7 of the Registrant's
               Registration Statement on Form S-1 (Registration No. 333-93853).

        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
7

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
8

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
9

                                   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 24,
2000.

                                    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 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 the
Registration Statement on Form S-8, filed with the Securities and Exchange
Commission on January 26, 2000, 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 24, 2000
Martine A. Rothblatt

/s/ James W. Crow                     President, Chief Operating Officer and
-----------------------------         Director                                 January 24, 2000
James W. Crow

/s/ Gilles Cloutier                   Chief Financial Officer, Chief
-----------------------------         Accounting Officer, Executive Vice
Gilles Cloutier                       President, Treasurer and Director        January 24, 2000
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10
SIGNATURE                                 TITLE                              DATE
/s/ Shelmer D. Blackburn, Jr.         Vice President of Operations,
-----------------------------         Secretary and Director                   January 24, 2000
Shelmer D. Blackburn, Jr.

/s/ Jean Guy-Lambert                  Director                                 January 24, 2000
-----------------------------
Jean Guy-Lambert

/s/ Noah A. Samara                    Director                                 January 24, 2000
-----------------------------
Noah A. Samara

/s/ David Gooray                      Director                                 January 24, 2000
-----------------------------
David Gooray

/s/ Olivia Giscard d'Estaing          Director                                 January 24, 2000
-----------------------------
Olivia Giscard d'Estaing
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