<PAGE>

    As filed with the Securities and Exchange Commission on August 24, 2000
                                                   Registration No. 333-________
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D. C. 20549

                                ______________

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

                              ___________________

                           OPNET TECHNOLOGIES, INC.
            (Exact name of registrant as specified in its charter)

                              ___________________

         Delaware                                               52-1483235
(State or other jurisdiction of                              (I.R.S. Employer
incorporation or organization)                            Identification Number)

                         ____________________________

                        3400 International Drive, N.W.
                            Washington, D.C. 20008
                                (202) 364-4700
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

             AMENDED AND RESTATED 1993 INCENTIVE STOCK OPTION PLAN
                           2000 STOCK INCENTIVE PLAN
                       2000 EMPLOYEE STOCK PURCHASE PLAN
                        2000 DIRECTOR STOCK OPTION PLAN
                           (Full title of the Plans)


                                 Marc A. Cohen
               Chairman of the Board and Chief Executive Officer
                           OPNET TECHNOLOGIES, INC.
                        3400 International Drive, N.W.
                            Washington, D.C. 20008
                                (202) 364-4700
  (Name and address, including zip code, and telephone number, including area
                          code, of agent for service)
<PAGE>

                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
----------------------------------------------------------------------------------------------------
                                  Number of     Proposed maximum     Proposed maximum    Amount of
     Title of securities          shares to      offering price     aggregate offering  registration
      to be registered          be registered       per share             price             fee
----------------------------------------------------------------------------------------------------
<S>                             <C>            <C>                  <C>                 <C>
 Amended and Restated              1,733,701        $  3.39 (1)           $ 5,877,246       $ 1,552
 1993 Incentive Stock
     Option Plan
Common Stock, $.001 par
   value per share
----------------------------------------------------------------------------------------------------
2000 Stock Incentive Plan          2,925,000        $ 22.875(2)           $66,909,375       $17,664
  2000 Employee Stock
     Purchase Plan
  2000 Director Stock
      Option Plan
 Common Stock, $.001 par
    value per share
----------------------------------------------------------------------------------------------------
                                                             Aggregate registration fee:    $19,216
</TABLE>

(1)  Estimated solely for the purposes of calculating the registration fee, and
     based upon the weighted average exercise price of outstanding options in
     accordance with Rule 457(h) under the Securities Act of 1933, as amended
     (the "Securities Act").
(2)  Estimated solely for the purpose of calculating the registration fee, and
     based upon the average of the high and low sale prices of the Registrant's
     Common Stock on the Nasdaq National Market on August 22, 2000 in accordance
     with Rules 457(c) and 457(h) of the Securities Act.
<PAGE>

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

     The information required by Part I is included in documents sent or given
to participants in the Amended and Restated 1993 Incentive Stock Option Plan,
the 2000 Stock Incentive Plan, the 2000 Employee Stock Purchase Plan and the
2000 Director Stock Option Plan of OPNET Technologies, Inc. (the "Registrant"),
pursuant to Rule 428(b)(1) under the Securities Act

PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3.  Incorporation of Documents by Reference.
              ---------------------------------------

     The Registrant is subject to the informational and reporting requirements
of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act") and in accordance therewith files reports, proxy
statements and other information with the Securities and Exchange Commission
(the "Commission"). The following documents, which are on file with the
Commission, are incorporated in this Registration Statement by reference:

      (a) The Registrant's latest annual report filed pursuant to Section 13(a)
or 15(d) of the Exchange Act or the latest prospectus filed pursuant to Rule
424(b) under the Securities Act that contains audited financial statements for
the Registrant's latest fiscal year for which such statements have been filed.

      (b) All other reports filed pursuant to Section 13(a) or 15(d) of the
Exchange Act since the end of the fiscal year covered by the document referred
to in (a) above.

      (c) The description of the common stock of the Registrant, $.001 par value
per share (the "Common Stock"), which is contained in the Registration Statement
on Form 8-A filed by the Registrant with the Commission on June 30, 2000,
including any amendment or report filed for the purpose of updating such
description.

     All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing of a post-
effective amendment which indicates that all shares offered hereby have been
sold or which deregisters all shares then remaining unsold, shall be deemed to
be incorporated in this Registration Statement by reference 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 by reference herein shall be
deemed to be modified or superseded for the purposes of this Registration
Statement to the extent a statement contained herein or in any other
subsequently filed document which also is or is deemed to be incorporated by
reference herein modifies or supersedes such statement. Any 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.

     Item 5.  Interests of Named Experts and Counsel.
              --------------------------------------

     Not Applicable.
<PAGE>

     Item 6.  Indemnification of Directors and Officers.
              -----------------------------------------

     The Registrant's Third Amended and Restated Certificate of Incorporation
(the "Certificate") provides that, except to the extent prohibited by the
Delaware General Corporation Law (the "DGCL"), the Registrant's directors shall
not be personally liable to the Registrant or its stockholders for monetary
damages for any breach of fiduciary duty as directors of the Registrant. Under
the DGCL, the directors have a fiduciary duty to the Registrant which is not
eliminated by this provision of the Certificate and, in appropriate
circumstances, equitable remedies such as injunctive or other forms of
nonmonetary relief will remain available. In addition, each director will
continue to be subject to liability under the DGCL for breach of the director's
duty of loyalty to the Registrant, for acts or omissions which are found by a
court of competent jurisdiction to be not in good faith or involving intentional
misconduct, for knowing violations of law, for actions leading to improper
personal benefit to the director, and for payment of dividends or approval of
stock repurchases or redemptions that are prohibited by the DGCL. This provision
also does not affect the directors' responsibilities under any other laws, such
as the federal securities laws or state or federal environmental laws. The
Registrant has obtained liability insurance for its officers and directors.

     Section 145 of the DGCL empowers a corporation to indemnify its directors
and officers and to purchase insurance with respect to liability arising out of
their capacity or status as directors and officers, provided that this provision
shall not eliminate or limit the liability of a director: (i) for any breach of
the director's duty of loyalty to the corporation or its stockholders, (ii) for
acts or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) arising under Section 174 of the DGCL including
for an unlawful payment of dividend or unlawful stock purchase or redemption or
(iv) for any transaction from which the director derived an improper personal
benefit. The DGCL provides further that the indemnification permitted thereunder
shall not be deemed exclusive of any other rights to which the directors and
officers may be entitled under the corporation's by-laws, any agreement, a vote
of stockholders or otherwise. The Certificate eliminates the personal liability
of directors to the fullest extent permitted by the DGCL and, together with the
Registrant's Amended and Restated By-Laws, provides that the Registrant shall
fully indemnify any person who was or is a party or is threatened to be made a
party to any threatened, pending or completed action, suit or proceeding
(whether civil, criminal, administrative or investigative) by reason of the fact
that such person is or was a director or officer of the Registrant, or is or was
serving at the request of the Registrant as a director or officer of another
corporation, partnership, joint venture, trust, employee benefit plan or other
enterprise, against expenses (including attorney's fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by such person in
connection with such action, suit or proceeding.

     Item 7.  Exemption from Registration Claimed.
              -----------------------------------

     Not applicable.

     Item 8.  Exhibits.
              --------

     The Exhibit Index immediately preceding the exhibits is attached hereto and
incorporated herein by reference.

     Item 9.  Undertakings.
              ------------

     1.  The Registrant hereby undertakes:

      (a)  To file, during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement to include any material
information with respect to the plan of
<PAGE>

distribution not previously disclosed in the Registration Statement or any
material change to such information in the Registration Statement.

      (b)  That, for the purpose of determining any liability under the
Securities Act, 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.

      (c)  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.

     2.  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) 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 the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

     3.  Insofar as indemnification for liabilities arising under the Securities
Act 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 Commission such indemnification is
against public policy as expressed in the Securities 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 whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
<PAGE>

                                  SIGNATURES

     Pursuant to the requirements of the Securities Act, 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 Washington, D.C. on August 23, 2000.

                              OPNET TECHNOLOGIES, INC.

                              By:  /s/ Marc A. Cohen
                                   ---------------------------------------------
                                    Marc A. Cohen
                                    Chairman of the Board and Chief Executive
                                    Officer

                               POWER OF ATTORNEY

     We, the undersigned officers and directors of OPNET Technologies, Inc.,
hereby severally constitute Marc A. Cohen, Alain J. Cohen, Joseph F. Greeves and
Brent B. Siler, and each of them singly, our true and lawful attorneys with full
power to them, and each of them singly, to sign for us and in our names in the
capacities indicated below, the Registration Statement on Form S-8 filed
herewith and any and all subsequent amendments to said Registration Statement,
and generally to do all such things in our names and behalf in our capacities as
officers and directors to enable OPNET Technologies, Inc. to comply with all
requirements of the Securities and Exchange Commission, hereby ratifying and
confirming our signatures as they may be signed by said attorneys, or any of
them, to said Registration Statement and any and all amendments thereto.

     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed below by the following persons in the capacities and
on the dates indicated.

<TABLE>
<CAPTION>
Signature                        Title                                              Date
---------                        -----                                              ----
<S>                             <C>                                             <C>
/s/ Marc A. Cohen               Chairman of the Board and                       August 23, 2000
--------------------------
Marc A. Cohen                   Chief Executive Officer
                                (Principal Executive Officer)


/s/ Alain J. Cohen              President, Chief Technology Officer             August 23, 2000
--------------------------
Alain J. Cohen                  and Director

/s/ Joseph F. Greeves           Senior Vice President of Finance and            August 23, 2000
--------------------------
Joseph F. Greeves               Chief Financial Officer
                                (Principal Financial and Accounting Officer)

/s/ Bruce R. Evans              Director                                        August 23, 2000
--------------------------
Bruce R. Evans
</TABLE>

<PAGE>

<TABLE>
<S>                             <C>                                             <C>
/s/ Steven G. Finn              Director                                        August 23, 2000
--------------------------
Steven G. Finn

/s/ William F. Stasior          Director                                        August 23, 2000
--------------------------
William F. Stasior
</TABLE>
<PAGE>

                                 EXHIBIT INDEX

Exhibit
Number      Description
------      -----------
4           Specimen Certificate of Common Stock of the Registrant is
            incorporated by reference to the Registrant's Registration Statement
            on Form S-1 (File No. 333-32588)
5           Opinion of Hale and Dorr LLP
23.1        Consent of Deloitte & Touche LLP
23.2        Consent of Hale and Dorr LLP (included in Exhibit 5)
24          Power of Attorney (included on the signature page of this
            Registration Statement)
[{"type": "S-8", "sequence": "1", "filename": "0001.txt", "description": "FORM S-8", "secsgml_size_bytes": 17406}]
{"company-data": {"conformed-name": "OPNET TECHNOLOGIES INC", "cik": "0001108924", "assigned-sic": "7373", "irs-number": "521483235", "state-of-incorporation": "DE", "fiscal-year-end": "0331"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-44430", "film-number": "709150"}, "business-address": {"street1": "3400 INTERNATIONAL DRIVE N.W.", "city": "WASHINGTON", "state": "DC", "zip": "20008", "phone": "2023644700"}, "mail-address": {"street1": "3400 INTERNATIONAL DRIVE, N.W.", "city": "WASHINGTON", "state": "DC", "zip": "20008"}}
As filed with the Securities and Exchange Commission on August 24, 2000
                                                   Registration No. 333-________
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D. C. 20549

                                ______________

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

                              ___________________

                           OPNET TECHNOLOGIES, INC.
            (Exact name of registrant as specified in its charter)

                              ___________________

         Delaware                                               52-1483235
(State or other jurisdiction of                              (I.R.S. Employer
incorporation or organization)                            Identification Number)

                         ____________________________

                        3400 International Drive, N.W.
                            Washington, D.C. 20008
                                (202) 364-4700
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

             AMENDED AND RESTATED 1993 INCENTIVE STOCK OPTION PLAN
                           2000 STOCK INCENTIVE PLAN
                       2000 EMPLOYEE STOCK PURCHASE PLAN
                        2000 DIRECTOR STOCK OPTION PLAN
                           (Full title of the Plans)

                                 Marc A. Cohen
               Chairman of the Board and Chief Executive Officer
                           OPNET TECHNOLOGIES, INC.
                        3400 International Drive, N.W.
                            Washington, D.C. 20008
                                (202) 364-4700
  (Name and address, including zip code, and telephone number, including area
                          code, of agent for service)
CALCULATION OF REGISTRATION FEE
----------------------------------------------------------------------------------------------------
                                  Number of     Proposed maximum     Proposed maximum    Amount of
     Title of securities          shares to      offering price     aggregate offering  registration
      to be registered          be registered       per share             price             fee
----------------------------------------------------------------------------------------------------
Amended and Restated              1,733,701        $  3.39 (1)           $ 5,877,246       $ 1,552
 1993 Incentive Stock
     Option Plan
Common Stock, $.001 par
   value per share
----------------------------------------------------------------------------------------------------
2000 Stock Incentive Plan          2,925,000        $ 22.875(2)           $66,909,375       $17,664
  2000 Employee Stock
     Purchase Plan
  2000 Director Stock
      Option Plan
 Common Stock, $.001 par
    value per share
----------------------------------------------------------------------------------------------------
                                                             Aggregate registration fee:    $19,216
(1)  Estimated solely for the purposes of calculating the registration fee, and
     based upon the weighted average exercise price of outstanding options in
     accordance with Rule 457(h) under the Securities Act of 1933, as amended
     (the "Securities Act").
(2)  Estimated solely for the purpose of calculating the registration fee, and
     based upon the average of the high and low sale prices of the Registrant's
     Common Stock on the Nasdaq National Market on August 22, 2000 in accordance
     with Rules 457(c) and 457(h) of the Securities Act.
PART I.  INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

     The information required by Part I is included in documents sent or given
to participants in the Amended and Restated 1993 Incentive Stock Option Plan,
the 2000 Stock Incentive Plan, the 2000 Employee Stock Purchase Plan and the
2000 Director Stock Option Plan of OPNET Technologies, Inc. (the "Registrant"),
pursuant to Rule 428(b)(1) under the Securities Act

PART II.  INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3.  Incorporation of Documents by Reference.
              ---------------------------------------

     The Registrant is subject to the informational and reporting requirements
of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of 1934, as
amended (the "Exchange Act") and in accordance therewith files reports, proxy
statements and other information with the Securities and Exchange Commission
(the "Commission"). The following documents, which are on file with the
Commission, are incorporated in this Registration Statement by reference:

      (a) The Registrant's latest annual report filed pursuant to Section 13(a)
or 15(d) of the Exchange Act or the latest prospectus filed pursuant to Rule
424(b) under the Securities Act that contains audited financial statements for
the Registrant's latest fiscal year for which such statements have been filed.

      (b) All other reports filed pursuant to Section 13(a) or 15(d) of the
Exchange Act since the end of the fiscal year covered by the document referred
to in (a) above.

      (c) The description of the common stock of the Registrant, $.001 par value
per share (the "Common Stock"), which is contained in the Registration Statement
on Form 8-A filed by the Registrant with the Commission on June 30, 2000,
including any amendment or report filed for the purpose of updating such
description.

     All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing of a post-
effective amendment which indicates that all shares offered hereby have been
sold or which deregisters all shares then remaining unsold, shall be deemed to
be incorporated in this Registration Statement by reference 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 by reference herein shall be
deemed to be modified or superseded for the purposes of this Registration
Statement to the extent a statement contained herein or in any other
subsequently filed document which also is or is deemed to be incorporated by
reference herein modifies or supersedes such statement. Any 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.

     Item 5.  Interests of Named Experts and Counsel.
              --------------------------------------

     Not Applicable.
Item 6.  Indemnification of Directors and Officers.
              -----------------------------------------

     The Registrant's Third Amended and Restated Certificate of Incorporation
(the "Certificate") provides that, except to the extent prohibited by the
Delaware General Corporation Law (the "DGCL"), the Registrant's directors shall
not be personally liable to the Registrant or its stockholders for monetary
damages for any breach of fiduciary duty as directors of the Registrant. Under
the DGCL, the directors have a fiduciary duty to the Registrant which is not
eliminated by this provision of the Certificate and, in appropriate
circumstances, equitable remedies such as injunctive or other forms of
nonmonetary relief will remain available. In addition, each director will
continue to be subject to liability under the DGCL for breach of the director's
duty of loyalty to the Registrant, for acts or omissions which are found by a
court of competent jurisdiction to be not in good faith or involving intentional
misconduct, for knowing violations of law, for actions leading to improper
personal benefit to the director, and for payment of dividends or approval of
stock repurchases or redemptions that are prohibited by the DGCL. This provision
also does not affect the directors' responsibilities under any other laws, such
as the federal securities laws or state or federal environmental laws. The
Registrant has obtained liability insurance for its officers and directors.

     Section 145 of the DGCL empowers a corporation to indemnify its directors
and officers and to purchase insurance with respect to liability arising out of
their capacity or status as directors and officers, provided that this provision
shall not eliminate or limit the liability of a director: (i) for any breach of
the director's duty of loyalty to the corporation or its stockholders, (ii) for
acts or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) arising under Section 174 of the DGCL including
for an unlawful payment of dividend or unlawful stock purchase or redemption or
(iv) for any transaction from which the director derived an improper personal
benefit. The DGCL provides further that the indemnification permitted thereunder
shall not be deemed exclusive of any other rights to which the directors and
officers may be entitled under the corporation's by-laws, any agreement, a vote
of stockholders or otherwise. The Certificate eliminates the personal liability
of directors to the fullest extent permitted by the DGCL and, together with the
Registrant's Amended and Restated By-Laws, provides that the Registrant shall
fully indemnify any person who was or is a party or is threatened to be made a
party to any threatened, pending or completed action, suit or proceeding
(whether civil, criminal, administrative or investigative) by reason of the fact
that such person is or was a director or officer of the Registrant, or is or was
serving at the request of the Registrant as a director or officer of another
corporation, partnership, joint venture, trust, employee benefit plan or other
enterprise, against expenses (including attorney's fees), judgments, fines and
amounts paid in settlement actually and reasonably incurred by such person in
connection with such action, suit or proceeding.

     Item 7.  Exemption from Registration Claimed.
              -----------------------------------

     Not applicable.

     Item 8.  Exhibits.
              --------

     The Exhibit Index immediately preceding the exhibits is attached hereto and
incorporated herein by reference.

     Item 9.  Undertakings.
              ------------

     1.  The Registrant hereby undertakes:

      (a)  To file, during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement to include any material
information with respect to the plan of
distribution not previously disclosed in the Registration Statement or any
material change to such information in the Registration Statement.

      (b)  That, for the purpose of determining any liability under the
Securities Act, 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.

      (c)  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.

     2.  The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) 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 the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

     3.  Insofar as indemnification for liabilities arising under the Securities
Act 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 Commission such indemnification is
against public policy as expressed in the Securities 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 whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
SIGNATURES

     Pursuant to the requirements of the Securities Act, 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 Washington, D.C. on August 23, 2000.

                              OPNET TECHNOLOGIES, INC.

                              By:  /s/ Marc A. Cohen
                                   ---------------------------------------------
                                    Marc A. Cohen
                                    Chairman of the Board and Chief Executive
                                    Officer

                               POWER OF ATTORNEY

     We, the undersigned officers and directors of OPNET Technologies, Inc.,
hereby severally constitute Marc A. Cohen, Alain J. Cohen, Joseph F. Greeves and
Brent B. Siler, and each of them singly, our true and lawful attorneys with full
power to them, and each of them singly, to sign for us and in our names in the
capacities indicated below, the Registration Statement on Form S-8 filed
herewith and any and all subsequent amendments to said Registration Statement,
and generally to do all such things in our names and behalf in our capacities as
officers and directors to enable OPNET Technologies, Inc. to comply with all
requirements of the Securities and Exchange Commission, hereby ratifying and
confirming our signatures as they may be signed by said attorneys, or any of
them, to said Registration Statement and any and all amendments thereto.

     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed below by the following persons in the capacities and
on the dates indicated.
Signature                        Title                                              Date
---------                        -----                                              ----
/s/ Marc A. Cohen               Chairman of the Board and                       August 23, 2000
--------------------------
Marc A. Cohen                   Chief Executive Officer
                                (Principal Executive Officer)

/s/ Alain J. Cohen              President, Chief Technology Officer             August 23, 2000
--------------------------
Alain J. Cohen                  and Director

/s/ Joseph F. Greeves           Senior Vice President of Finance and            August 23, 2000
--------------------------
Joseph F. Greeves               Chief Financial Officer
                                (Principal Financial and Accounting Officer)

/s/ Bruce R. Evans              Director                                        August 23, 2000
--------------------------
Bruce R. Evans
/s/ Steven G. Finn              Director                                        August 23, 2000
--------------------------
Steven G. Finn

/s/ William F. Stasior          Director                                        August 23, 2000
--------------------------
William F. Stasior
EXHIBIT INDEX

Exhibit
Number      Description
------      -----------
4           Specimen Certificate of Common Stock of the Registrant is
            incorporated by reference to the Registrant's Registration Statement
            on Form S-1 (File No. 333-32588)
5           Opinion of Hale and Dorr LLP
23.1        Consent of Deloitte & Touche LLP
23.2        Consent of Hale and Dorr LLP (included in Exhibit 5)
24          Power of Attorney (included on the signature page of this
            Registration Statement)