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                                                                   EXHIBIT 4.3


                             PRA INTERNATIONAL, INC.
                       1997 STOCK OPTION PLAN, AS AMENDED


         1.       Definitions. As used in this 1997 Stock Option Plan of PRA
International, Inc., the following terms shall have the following meanings:

                  1.1.     Board means the Company's Board of Directors.

                  1.2.     Code means the federal Internal Revenue Code of 1986,
         as amended.

                  1.3.     Committee means the compensation committee appointed
         by the Board. Such Committee shall be responsible for the
         administration of the Plan, as provided in Section 5 of the Plan.

                  1.4.     Company means PRA International, Inc., a Delaware
         corporation.

                  1.5.     Consulting Agreement means a consulting agreement, if
         any, between the Company and an Optionee, setting forth, inter alia,
         conditions and restrictions upon the transfer of shares of Stock.

                  1.6.     Employment Agreement means an employment agreement,
         if any, between the Company and an Optionee, setting forth, inter alia,
         conditions and restrictions upon the transfer of shares of Stock.

                  1.7.     Fair Market Value means the value of a share of Stock
         on any date as determined by the Committee.

                  1.8.     Grant Date means the date as of which an Option is
         granted, as determined under Section 7.

                  1.9.     Immediate Family Member means, with respect to any
         Optionee, such Optionee's spouse and lineal descendants or any trust
         for the benefit of, or the legal representative of, any of the
         preceding persons.

                  1.10.    Incentive Option means an Option which by its terms
         is to be treated as an "incentive stock option" within the meaning of
         Section 422 of the Code.


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                  1.11.    Non-statutory Option means any Option that is not an
         Incentive Option.

                  1.12.    Option means an option to purchase shares of Stock
         granted under the Plan.

                  1.13.    Option Agreement means an agreement between the
         Company and an Optionee, setting forth the terms and conditions of an
         Option.

                  1.14.    Option Price means the price paid by an Optionee for
         a share of Stock upon exercise of an Option.

                  1.15.    Optionee means a person eligible to receive an
         Option, as provided in Section 6 of the Plan, to whom an Option shall
         have been granted under the Plan.

                  1.16.    Plan means this 1997 Stock Option Plan of the
         Company, as amended from time to time.

                  1.17.    Stock means Common Stock, par value $0.01 per share,
         of the Company.

                  1.18.    Stock Restriction Agreement means a Stock Restriction
         Agreement entered into by the Company and an Optionee pursuant to
         Section 5 hereof.

                  1.19.    Ten Percent Owner means a person who owns, or is
         deemed within the meaning of Section 422(b)(6) of the Code to own,
         stock possessing more than ten percent (10%) of the total combined
         voting power of all classes of stock of the Company (or its parent or
         subsidiary corporations). Whether a person is a Ten Percent Owner shall
         be determined with respect to each Option based on the facts existing
         immediately prior to the Grant Date of such Option.

                  1.20.    Vesting Year for any portion of any Incentive Option
         means the calendar year in which that portion of the Option first
         becomes exercisable.

         2.       Purpose. This Plan is intended to encourage ownership of Stock
by employees, consultants, and unaffiliated non-employee directors of the
Company and its subsidiaries and to provide additional incentives for them to
promote the success of the Company's business. The Plan is intended to be an
incentive stock option plan within the meaning of Section 422 of the Code but
not all Options granted hereunder are required to be Incentive Options.


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         3.       Term of the Plan. Options may be granted hereunder at any time
during the period commencing upon the approval of the Plan by the Board and
ending January 31, 2007.

         4.       Stock Subject to the Plan. At no time shall the number of
shares of Stock then outstanding which are attributable to the exercise of
Options granted under the Plan, plus the number of shares then issuable upon
exercise of outstanding Options granted under the Plan, exceed one million one
hundred thousand (1,100,000) shares, subject, however, to the provisions of
Section 17 of the Plan. Shares to be issued upon the exercise of Options granted
under the Plan may be either authorized but unissued shares or shares held by
the Company in its treasury. If any Option expires or terminates for any reason
without having been exercised in full, the shares not purchased thereunder shall
again be available for Options thereafter to be granted.

         5.       Administration. The Plan shall be administered by the
Committee. Subject to the provisions of the Plan, the Committee shall have
complete authority, in its discretion, to make or to select the manner of making
the following determinations with respect to each Option to be granted by the
Company: (a) the employee, consultant, or unaffiliated non-employee director to
receive the Option; (b) whether the Option (if granted to an employee) will be
an Incentive Option or Non-statutory Option; (c) the time of granting the
Option; (d) the number of shares subject to the Option provided; however, that
in no event shall any Optionee be granted in any calendar year Options to
purchase more than ninety-eight thousand five hundred (98,500) shares; (e) the
Option Price; (f) the Option period; (g) the Option exercise date or dates or,
if the Option is immediately exercisable in full on its Grant Date, the vesting
schedule, if any, applicable to the shares of Stock issuable upon the exercise
of the Option; and (h) the effect of termination of employment, consulting or
association with the Company on the subsequent exercisability of the Option. In
making such determinations, the Committee may take into account the nature of
the services rendered by the respective employees and consultants, their present
and potential contributions to the success of the Company and its subsidiaries,
and such other factors as the Committee in its discretion shall deem relevant.
Subject to the provisions of the Plan, the Committee shall also have complete
authority to interpret the Plan, to prescribe, amend and rescind rules and
regulations relating to it, to determine the terms and provisions of the
respective Option Agreements (which need not be identical), and to make all
other determinations necessary or advisable for the administration of the Plan.
The Committee shall also have complete authority in its discretion to require
that, as a condition precedent to the grant or exercise of any Option, the
Optionee shall enter into a Stock Restriction Agreement with the Company,
containing such terms, provisions and conditions as the Committee shall
determine in its absolute discretion, including, without limitation, provisions
relating to the vesting of shares of Stock issuable upon exercise of an Option
and provisions imposing restrictions upon the transferability of any and all
shares of Stock or other capital stock of the


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Company owned of record or beneficially by the Optionee party thereto. The
Committee's determinations on the matters referred to in this Section 5 shall be
conclusive.

         6.       Eligibility. An Option may be granted under the Plan only to
an employee, consultant, or unaffiliated non-employee director of one or more of
the Company or any subsidiary thereof.

         7.       Time of Granting Options. The granting of an Option shall take
place at the time specified in the Option Agreement. Only if expressly so
provided in the Option Agreement, shall the Grant Date be the date on which an
Option Agreement shall have been duly executed and delivered by the Company and
the Optionee.

         8.       Option Price. The Option Price under each Incentive Option
shall be not less than 100% of the Fair Market Value of Stock on the Grant Date,
or not less than 110% of the Fair Market Value of Stock on the Grant Date if the
Optionee is a Ten Percent Owner. The Option Price under each Non-statutory
Option shall not be so limited solely by reason of this Section 8.

         9.       Option Period. No Incentive Option may be exercised later than
the tenth anniversary of the Grant Date, but in any case not later than the
fifth anniversary of the Grant Date if the Optionee is a Ten Percent Owner. The
option period under each Non-statutory Option shall not be so limited solely by
reason of this Section 9. An Option may become exercisable in such installments,
cumulative or non-cumulative, as the Committee may determine. In the case of an
Option not otherwise immediately exercisable in full, the Committee may
accelerate the exercisability of such Option in whole or in part at any time,
provided the acceleration of the exercisability of any Incentive Option would
not cause the Option to fail to comply with the provisions of Section 422 of the
Code.

         10.      Limit on Incentive Option Characterization. No Incentive
Option shall be considered an Incentive Option to the extent that pursuant to
its terms it would permit the Optionee to purchase for the first time in any
Vesting Year under that Incentive Option more than the number of shares of Stock
calculated by dividing the current limit by the Option Price. The current limit
for any Optionee for any Vesting Year shall be $100,000 minus the aggregate Fair
Market Value at the date of grant of the number of shares of Stock available for
purchase for the first time in the Vesting Year under each other Incentive
Option granted to the Optionee under the Plan and each other incentive stock
option granted to the Optionee under any other incentive stock option plan of
the Company (and any parent and subsidiary corporations).

         11.      Exercise of Option. An Option may be exercised by the Optionee
giving written notice, in the manner provided in Section 21, specifying the
number of shares with respect to which the Option is then being exercised. The
notice shall


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be accompanied by payment in the form of cash, or certified or bank check
payable to the order of the Company, in an amount equal to the aggregate Option
Price of the shares to be purchased. Receipt by the Company of such notice and
payment, and, if applicable, the Optionee's executed counterpart of any Stock
Restriction Agreement required by the Committee pursuant to Section 5 hereof,
shall constitute the exercise of the Option. Within thirty (30) days thereafter
but subject to the remaining provisions of the Plan, the Company shall deliver
or cause to be delivered to the Optionee or his agent a certificate or
certificates for the number of shares then being purchased. Such shares shall be
fully paid and nonassessable.

         12.      Restrictions on Issue of Shares.

                  (a)      Notwithstanding any other provision of the Plan, if,
at any time, in the reasonable opinion of the Company, the issuance of shares of
Stock covered by the exercise of any Option may constitute a violation of law,
then the Company may delay such issuance and the delivery of a certificate for
such shares until (i) approval shall have been obtained from such governmental
agencies, other than the Securities and Exchange Commission, as may be required
under any applicable law, rule, or regulation; and (ii) in the case where such
issuance would constitute a violation of a law administered by or a regulation
of the Securities and Exchange Commission, one of the following conditions shall
have been satisfied:

                  (1)      the shares with respect to which such Option has been
         exercised are at the time of the issue of such shares effectively
         registered under the Securities Act of 1933, as amended (the
         "Securities Act"); or

                  (2)      a no-action letter in form and substance reasonably
         satisfactory to the Company and its counsel with respect to the
         issuance of such shares shall have been obtained by the Company from
         the Securities and Exchange Commission.

The Company shall make all reasonable efforts to bring about the occurrence of
said events.

                  (b)      Each certificate representing shares issued upon the
exercise of an Option will bear restrictive legends which may refer to this Plan
and to applicable restrictions under any Employment Agreement, Consulting
Agreement or Stock Restriction Agreement, as applicable.

         13.      Purchase for Investment; Subsequent Registration.

                  (a)      Without limiting the generality of Section 12 hereof,
if the shares to be issued upon exercise of an Option granted under the Plan
have not been effectively registered under the Securities Act, the Company shall
be under no obligation to issue any shares covered by any Option unless the
person who

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exercises such Option, in whole or in part, shall give a written representation
to the Company which is satisfactory in form and substance to its counsel and
upon which the Company may reasonably rely, that he or she is acquiring the
shares issued pursuant to such exercise of the Option as an investment and not
with a view to, or for sale in connection with, the distribution of any such
shares.

                  (b)      Each certificate representing shares of Stock issued
pursuant to the exercise of an Option granted pursuant to this Plan may bear a
reference to the investment representation made in accordance with this Section
13 and to the fact that no registration statement has been filed with the
Securities and Exchange Commission in respect of said Stock.

                  (c)      If the Company shall deem it necessary or desirable
to register under the Securities Act or other applicable statutes any shares
with respect to which an Option shall have been granted, or to qualify any such
shares for exemption from the Securities Act or other applicable statutes, then
the Company shall take such action at its own expense. The Company may require
from each Option holder, or each holder of shares of Stock acquired pursuant to
the Plan, such information in writing for use in any registration statement,
prospectus, preliminary prospectus or offering circular as is reasonably
necessary for such purpose and may require reasonable indemnity to the Company
and its officers and directors from such holder against all losses, claims,
damage and liabilities arising from such use of the information so furnished and
caused by any untrue statement of any material fact therein or caused by the
omission to state a material fact required to be stated therein or necessary to
make the statements therein not misleading in the light of the circumstances
under which they were made.

         14.      Withholding; Notice of Disposition of Stock Prior to
                  Expiration of Specified Holding Period.

                  (a)      Whenever shares are to be issued in satisfaction of
an Option granted hereunder, the Company shall have the right to require the
Optionee to remit to the Company an amount sufficient to satisfy federal, state,
local or other withholding tax requirements if and to the extent required by law
(whether so required to secure for the Company an otherwise available tax
deduction or otherwise) prior to the delivery of any certificate or certificates
for such shares.

                  (b)      The Company may require as a condition to the
issuance of shares covered by any Incentive Option that the party exercising
such Option give a written representation to the Company which is satisfactory
in form and substance to its counsel and upon which the Company may reasonably
rely, that he or she will report to the Company any disposition of such shares
prior to the expiration of the holding periods specified by Section 422(a)(1) of
the Code. If and to the extent that the realization of income in such a
disposition imposes upon the Company federal, state, local or other withholding
tax requirements, or any such withholding is

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required to secure for the Company an otherwise available tax deduction, the
Company shall have the right to require that the recipient remit to the Company
an amount sufficient to satisfy those requirements; and the Company may require
as a condition to the issuance of shares covered by an Incentive Option that the
party exercising such option give a satisfactory written representation
promising to make such a remittance.

         15.      Termination of Association with the Company.

                  (a)      Termination of Options. If the Optionee's employment,
consulting or other association or relationship with the Company or one of its
subsidiaries is terminated, whether voluntarily or otherwise, the Option, (i)
all unvested Options shall automatically terminate and (ii) to the extent the
Option is exercisable on the date of termination, may continue to be exercised
by the Optionee in accordance with its terms for a period of thirty (30) days
after such termination date. Notwithstanding the foregoing, in the event that
the applicable Option Agreement with respect to an Option shall contain specific
provisions governing the effect that any such termination shall have on the
exercisability of such Option, such provisions shall, to the extent that they
are inconsistent with the provisions of this Section 15, control and be deemed
to supersede the provisions of this Section 15. For purposes of this Section 15,
military or sick leave shall not be deemed a termination of employment, provided
that it does not exceed the longer of 30 days or the period during which the
absent Optionee's reemployment rights, if any, are guaranteed by statute or by
contract.

                  (b)      Buy-Back Provisions. The Options of any Optionee
shall be subject to the terms of any buy-back provisions contained in any
related Option Agreement, Stock Restriction Agreement, Employment Agreement or
Consulting Agreement to which such Optionee is a party.

         16.      Transferability of Options. Options shall not be transferable,
otherwise than by will or the laws of descent and distribution, and may be
exercised during the life of the Optionee only by the Optionee; provided,
however, that this Section shall not bar a transfer, assignment or sale of
Non-statutory Options by an Optionee to, or for the benefit of, such Optionee's
Immediate Family Members, who shall take and be entitled to exercise such
Non-statutory Options subject to all the limitations set forth in this Plan, the
applicable Option Agreement and the applicable Stock Restriction Agreement.
Notwithstanding anything in this Section 16 to the contrary, the Company shall
not recognize any transfer, assignment or sale by the Optionee of Non-statutory
Options to an Immediate Family Member, and any such Non-statutory Options
transferred, assigned or sold shall be deemed to be owned and held by such
Optionee rather than by the transferee, unless prior to any such transfer,
assignment or sale such transferee shall execute an Instrument of Adherence to
the applicable Option Agreement and to the applicable Stock Restriction
Agreement, and such Instrument of Adherence is in form and

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substance satisfactory to the Company. Notwithstanding the foregoing, the
Committee reserves the right in its sole and absolute discretion to approve or
disapprove any proposed transfer of Options otherwise permitted pursuant to the
foregoing provisions of this Section 16.

         17.      Adjustment of Number of Option Shares. In the event of any
stock dividend payable in Stock or any split-up or contraction in the number of
shares of Stock after the date of an Option Agreement and prior to the exercise
in full of the Option, the number of shares subject to such Option Agreement and
the price to be paid for each share subject to the Option shall be
proportionately adjusted. In the event of any reclassification or change of
outstanding shares of Stock or in case of any consolidation or merger of the
Company with or into another company or in case of any sale or conveyance to
another company or entity of the property of the Company as a whole or
substantially as a whole, shares of stock or other securities equivalent in kind
and value to those shares an Optionee would have received if he or she had held
the full number of shares of Stock subject to the Option immediately prior to
such reclassification, change, consolidation, merger, sale or conveyance and had
continued to hold those shares (together with all other shares, stock and
securities thereafter issued in respect thereof) to the time of the exercise of
the Option shall thereupon be subject to the Option. Upon dissolution or
liquidation of the Company, the Option shall terminate, but the Optionee (if at
the time in the employ of or retained as a consultant to the Company or any of
its subsidiaries) shall have the right, immediately prior to such dissolution or
liquidation, to exercise the Option to the extent exercisable on the date of
such dissolution or liquidation. No fraction of a share shall be purchasable or
deliverable upon exercise, but in the event any adjustment hereunder of the
number of shares covered by the Option shall cause such number to include a
fraction of a share, such number of shares shall be adjusted to the nearest
smaller whole number of shares. In the event of changes in the outstanding Stock
by reason of any stock dividend, split-up, contraction, reclassification, or
change of outstanding shares of Stock of the nature contemplated by this Section
17, the number of shares of Stock available for the purpose of the Plan as
stated in Section 4 hereof shall be correspondingly adjusted.

         18.      Reservation of Stock. The Company shall at all times during
the term of the Options reserve or otherwise keep available such number of
shares of Stock as will be sufficient to satisfy the requirements of the Plan
(if then in effect) and such Options shall pay all fees and expenses necessarily
incurred by the Company in connection therewith.

         19.      Limitation of Rights in Stock; No Special Employment or Other
Rights. The Optionee shall not be deemed for any purpose to be a stockholder of
the Company with respect to any of the shares of Stock covered by an Option,
except to the extent that the Option shall have been exercised with respect
thereto and, in addition, a certificate shall have been issued therefor and
delivered to the Optionee or his agent. Any Stock issued pursuant to the Option
shall be subject to all

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restrictions upon the transfer thereof which may be now or hereafter imposed by
the Certificate of Incorporation or the By-laws of the Company or by any
applicable Employment Agreement, Consulting Agreement or Stock Restriction
Agreement. Nothing contained in the Plan or in any Option shall confer upon any
Optionee any right with respect to the continuation of his or her employment
with, or retention as a consultant by, the Company (or any subsidiary), or
interfere in any way with the right of the Company (or any subsidiary), subject
to the terms of any separate employment or consulting agreement or provision of
law or corporate articles or by-laws to the contrary, at any time to terminate
such employment or consulting agreement or to increase or decrease the
compensation of the Optionee from the rate in existence at the time of the grant
of an Option.

         20.      Termination and Amendment of the Plan. The Board may at any
time terminate the Plan or make such modifications of the Plan as it shall deem
advisable. No termination or amendment of the Plan may, without the consent of
the Optionee to whom any Option shall theretofore have been granted, adversely
affect the rights of such Optionee under such Option.

         21.      Notices and Other Communications. All notices and other
communications required or permitted under the Plan shall be effective if in
writing and if delivered or sent by certified or registered mail, return receipt
requested (a) if to the Optionee, at his or her residence address last filed
with the Company, and (b) if to the Company, at PRA International, Inc.,
American Center, 8300 Boone Boulevard, Suite 310, Vienna, Virginia 22182,
Attention: President, or to such other persons or addresses as the Optionee or
the Company may specify by a written notice to the other from time to time.

         22.      Effective Date. This Plan shall be deemed effective as of July
24, 1997, the date upon which the Company's Board of Directors adopted this
Plan.