EXHIBIT 10.6


                            SHAREHOLDER'S AGREEMENT

         THIS  SHAREHOLDER'S  AGREEMENT,  made as of this 1st day of  September,
1990 by and among InforMax,  Inc., a Delaware  corporation (the  "Corporation"),
and Alexander  Titomirov  ("Titomirov"),  Valera Sagitov  ("Sagitov"),  James E.
Bernstein ("Bernstein"),  C. Bowdoin Train ("Train"),  Lewis Hecht ("Hecht") and
Brennan  Klose  ("Klose"),  all of whom are  sometimes  hereinafter  referred to
collectively as the "Shareholders."

                                   WITNESSETH

         WHEREAS, the Corporation has authorized Twenty Thousand (20,000) shares
of common  stock,  in two (2) classes,  the first class  consisting  of Thirteen
Thousand Five Hundred (13,500) shares of voting common stock, par value One Cent
($.01) per share, and the second consisting of Six Thousand Five Hundred (6,500)
shares of non-voting common stock, par value One Cent ($.01) per share;

         WHEREAS,  Titomirov owns Seven Thousand (7,000) voting shares,  Sagitov
owns One Thousand  Five Hundred  (1,500) each of voting and  non-voting  shares,
Train owns One  Thousand  (1,000)  non-voting  shares,  Hecht owns One  Thousand
(1,000)  non-voting  shares,  Klose  owns  Fifty  (50)  non-voting  shares,  and
Bernstein, upon conversion of his Revenue Participation Certificate ("RPC"),



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shall  receive One  Thousand  (1,000)  voting  shares and One  Thousand  (1,000)
non-voting shares;

          WHEREAS,  the Shareholders and the Corporation  desire to make certain
arrangements  with respect to such outstanding  shares (and any shares hereafter
acquired by any Shareholder) and the business and management of the Corporation;

          NOW,  THEREFORE,  in  consideration  of the  promises  and the  mutual
covenants contained herein, the parties agree as follows:

          1.   Definitions.

          As used in this Agreement, the following terms shall have the meanings
set forth in this Section 1:

               (a)   Shares - shares of voting or non-voting common stock of the
Corporation.

               (b)   Bona Fide Offer - a written offer  made in good faith by an
individual or entity,  unrelated to the  Shareholder  receiving  the offer,  and
having  sufficient  financial  resources to purchase the Shares specified in the
offer on the terms stated  therein, provided that (i) the name and residence and
business addresses of the offeror are stated in the offer, and (ii) the offer is
accompanied  by a deposit in the form of a certified  or  cashier's  check in an
amount equal to not less than ten percent (10%) of the proposed purchase price.

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               (c)   Disability - the inability of a Shareholder, due to illness
or injury, to perform at least fifteen (15) eight-hour days of work at an office
outside his home during any six (6) month period.  The date of Disability  shall
be determined in good faith by the Board of Directors of the Corporation.

               (d) Fair Market Value Per Share - the fair market value per Share
shall be determined  as of the date of an event of Separation  (or, in the event
of Separation  due to the death of a  Shareholder,  if the  Corporation  and the
Shareholders  have failed to exercise their option to purchase the Shares of the
deceased  Shareholder  and the eighteen month period during which the estate may
seek a buyer pursuant  hereto has expired,  then the fair market value per Share
shall be determined as of the date that the estate's legal  representative shall
have offered  such Shares to the  Corporation  for purchase  pursuant to Section
5(a)(ii)) by agreement  between the relevant  parties within thirty (30) days of
the effective  notice of such event of Separation (or, in the event of the offer
to the  Corporation  by  the  legal  representative  of a  Shareholder's  estate
described  above,  within thirty (30) days of the effective notice of such offer
to the Corporation), or if such parties cannot agree within such thirty (30) day
period, then by an appraiser approved in good faith by the Board of Directors of
this  Corporation  and  experienced  in  valuations  of companies  substantially
similar  to the  Corporation.  The  determination  of such  appraiser  shall  be
conclusive and binding upon the

                                      -3-


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parties  hereto, and shall not be subject to review by any arbitral, judicial or
other tribunal or authority.

               (e)  Family - a Shareholder's spouse, children, parents, siblings
or one or more trusts  established for the exclusive benefit of such Shareholder
and/or one or more of such persons.

               (f)  Separation  -  the  following  events:  Disability,   death,
Termination  For  Cause or any  other  event by which a  Shareholder  ceases  to
perform services for the Corporation.

               (g)  Termination  For Cause - shall mean  termination  for one or
more of the following:

                        (i)   The  commission  of  an  act  of  fraud  upon  the
               Corporation, its directors or shareholders, or any of its clients
               or customers, or the commission of any other act that jeopardizes
               the Corporation's right or ability to operate its business;

                        (ii)  The repeated  failure or refusal of a party hereto
               to perform the legitimate  duties assigned to him by the Board of
               Directors of the Corporation in its reasonable discretion;

                        (iii)  Incompetence,  misconduct  or  negligence in  the
               performance of the legitimate duties and

                                      -4-


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               responsibilities  from  time to time  assigned  to a party by the
               Board of Directors in its reasonable discretion;

                        (iv) The conviction of a party for a felony;

                        (v)  The undue  dependency  of  a  party  on  alcohol or
               drugs; or

                        (vi) The material breach of any of the provisions hereof
               by any party hereto.

          2.   Term of Agreement.

          This  Agreement  shall  continue  in full force and  effect  until the
earliest of (i) the date that only one Shareholder owns, directly or indirectly,
all of the Shares,  (ii) the date as of which the  Agreement  is  terminated  by
unanimous written agreement among the Corporation,  those parties hereto who are
shareholders  at the time of such  agreement and Bernstein so long as he has the
right to own Shares upon  conversion of the RPC at the time of such agreement or
(iii)  the  date  on  which  more  than  50% of  the  Corporation's  issued  and
outstanding  Shares have been  registered  under the  Securities Act of 1933, as
amended.  Except as may otherwise by expressly provided herein, upon termination
of this  Agreement,  each  Shareholder  shall  surrender to the  Corporation the
certificates  representing his Shares, and the Corporation shall issue to him in
lieu thereof new certificates which shall

                                      -5-


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bear no reference  to  this  Agreement or to any of the restrictions on transfer
set forth herein.

          3.   Voting of Shares.

          Unless Titomirov shall have ceased to own Shares of the  Corporation's
common stock or shall have experienced an event of Separation,  each Shareholder
hereby agrees to vote all voting Shares now or hereafter owned by him, either in
person or by proxy, at each election of directors of the  Corporation,  to elect
Titomirov.  Unless  Bernstein shall have ceased to hold the RPC or any Shares of
the Corporation's common stock into which the RPC has been converted,  or unless
he shall have experienced an event of Separation,  then each Shareholder  hereby
agrees to vote all voting Shares now or hereafter owned by him, either in person
or by  proxy,  at each  election  of  directors  of the  Corporation,  to  elect
Bernstein. Additional directors shall be elected from time to time in accordance
with the By-laws of the Corporation.

          4.   Restrictions on Transfer of Shares.

               (a)  Restrictions.  All  Shares  now  or  hereafter  owned  by  a
Shareholder shall be subject to an option to purchase,  a right of first refusal
and certain restrictions on transfer, all as set forth in this Agreement, and no
Shareholder  shall sell,  assign,  transfer,  pledge or  hypothecate  any Shares
except in accordance with the terms of this Agreement. No Shareholder

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shall  pledge  or  hypothecate  any  Shares  without  the prior  consent  of the
Corporation.  Any sale,  assignment,  transfer,  pledge or  hypothecation of any
Shares in violation of this Agreement shall be void, and the  Corporation  shall
not be obligated either to transfer such Shares on its books or to recognize any
such unauthorized transaction in any manner whatsoever.

               (b) Securities Laws. No Shareholder shall assign, deliver, pledge
or otherwise transfer any Shares, nor will any assignee,  pledgee or endorsee of
any Shares be  recognized as an owner of any Shares by the  Corporation  for any
purpose,  unless a Registration  Statement under the Securities Act of 1933 with
respect to such  Shares  shall then be in effect or unless any such  assignment,
delivery,  pledge  or  transfer  may be  made  without  registration  under  the
Securities Act of 1933, as amended,  and under any applicable  state  securities
laws, and such assignment or transfer will not adversely affect  the  exemptions
from securities  registration on which the Corporation  relied in selling Shares
to the Shareholders, all to the satisfaction of counsel to the Corporation.

               (c) Restrictive  Legend.  Each  certificate  representing  Shares
subject to this Agreement shall contain a legend on the fact thereof  indicating
that  transferability of such stock is restricted and an endorsement on the back
thereof which includes language in substantially the following form:

                                      -7-

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                     Any  sale,  pledge  or  other  disposition of the
              shares  of  stock  represented  by this  certificate  is
              restricted by and subject to the terms and provisions of
              the    Shareholders'    Agreement,     dated    as    of
              _________________,   1990,  as  such  Agreement  may  be
              amended from time to time, by and among the Corporation,
              the  holder  of  this   certificate  and  certain  other
              shareholders of the Corporation.

          5.  Option to Purchase Shares.

              (a) Exercise of Option in the Event of Death of a Shareholder.

                     (i)  In  the   event  of  death  of  a   Shareholder,   his
representative shall notify the Corporation and the surviving  Shareholders (the
"Surviving  Shareholders"), within ten (10) days after the  appointment  of such
representative,  that an event of Separation has occurred.  The  Corporation and
the Surviving  Shareholders  shall have the exclusive  option for six (6) months
from the  earlier  of (A) the date  that  notice of  Separation  is given to the
Corporation  and  the  Surviving  Shareholders  by  the  deceased  Shareholder's
representative  or (B) the  date  that the  Corporation  notifies  the  deceased
Shareholder's  representative  that  the  Corporation  is  taking  note  of  the
Separation,   to  purchase   all  (but  not  less  than  all)  of  the  deceased
Shareholder's  Shares in such  proportion as the  Corporation  and the Surviving
Shareholders shall agree. If the Corporation and the Surviving  Shareholders are
unable to so agree, then each Surviving Shareholder who wishes to participate in
such  purchase  shall have  priority  to  purchase  up to that  fraction  of the
deceased.

                                 -8-

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Shareholder's  Shares  in which  the  numerator  is the  number of Shares of the
Corporation's  common  stock  owned  by  such  Surviving   Shareholder  and  the
denominator is the number of Shares of the  Corporation's  common stock owned by
the Surviving  Shareholders  who desire to participate in such purchase.  In the
event  that not all of the  deceased  Shareholder's  Shares  would be  purchased
pursuant to the priority  allocations set forth in the previous  sentence,  then
the Corporation may first elect to purchase up to all of the remaining Shares of
the deceased  Shareholder.  If the Corporation fails to elect to purchase all of
such remaining  Shares,  then the Surviving  Shareholders who desire to purchase
the remaining  Shares shall deliver  written notice to the  Corporation  stating
therein  the number of such  remaining  Shares each such  Surviving  Shareholder
desires to  purchase.  The  remaining  Shares  shall be allocated in one or more
successive  allocations  to those  Surviving  Shareholders  who wish to purchase
additional  Shares and each such  allocation  shall be determined by a fraction,
the  numerator  of which is the  number of Shares  owned by each such  Surviving
Shareholder and the denominator  which is the number of Shares owned by all such
Surviving   Shareholders.   Bernstein   shall  not  be  considered  a  Surviving
Shareholder  for purposes  hereof  unless he shall have first  converted his RPC
into Shares pursuant to the terms thereof; provided, however, that if not all of
the deceased  Shareholder's Shares would be purchased pursuant to the provisions
hereof, then at the Corporation's

                                      -9-

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option in its sole discretion Bernstein may elect to purchase any such remaining
Shares. If within fifteen (15) days prior to the expiration of the six (6) month
option  provided  herein the Board of Directors of the  Corporation has not been
reasonably   satisfied   that  all  and  not  less  than  all  of  the  deceased
Shareholder's Shares will be purchased at a single closing pursuant to the terms
hereof,  the  Corporation  may elect to purchase any  remaining  Shares.  If the
Corporation and/or the Surviving  Shareholders fail to tender the purchase price
for all of the Shares  pursuant to the terms  provided in subsection  and (d) of
this Section 5, the option of the Corporation and/or the Surviving  Shareholders
to purchase the deceased Shareholder's Shares shall expire.

                     (ii) In the event that the Corporation and/or the Surviving
Shareholders fail to exercise the option to purchase the deceased  Shareholder's
Shares in  accordance  with  paragraph  (i) of this Section  5(a),  the deceased
Shareholder's  representative shall be free, for a period of up to eighteen (18)
months,  to seek a buyer for the Shares,  subject to the right of first  refusal
provided for in Section 6 hereof. At the end of such eighteen (18) month period,
the  representative  shall offer all of such Shares to the  Corporation  and the
Corporation  shall  purchase all of such Shares.  The price and terms of payment
for such Shares shall be as provided in subjection (d) of this Section 5, except
that the  schedule  of payments of  principal  and  interest to be made over the
applicable five (5) year period

                                      -10-

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shall be determined by the Corporation at the time the Corporation purchases the
Shares;  provided,  however,  that the  schedule of payments  of  principal  and
interest  shall  not  be  less  advantageous  to  the  estate  of  the  deceased
Shareholder than is reasonably  practicable for the Corporation  considering the
Corporation's  financial condition at the time of the purchase.  The Corporation
may permit the Surviving Shareholders to participate in any purchase required by
this paragraph  (ii) of this Section 5(a) on the same terms as the  Corporation,
and in such proportion as are consonant with the priority  allocation  mechanism
set forth in paragraph (i) of this Section 5(a).

         (b)   Exercise of Option in the Event of Separation Other Than Death or
               Termination  For Cause Within Two Years of the Effective  Date of
               This Agreement.

                   (i) A  Shareholder  or his  representative  shall  notify the
Corporation,  and the other Shareholders (the "Remaining Shareholders") who have
not been subject to an event of  Separation,  that an event of  Separation  with
respect to such  Shareholder  (other than death or Termination  For Cause within
two years of the effective date of this  Agreement) has occurred within ten (10)
days after such  event,  except  that if such  event (for  example,  Disability)
requires the appointment of a representative for the selling  Shareholder,  such
notice  shall be given  within  ten (10)  days  after  the  appointment  of such
representative. The Corporation and the Remaining Shareholders shall have

                                      -11-

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the  exclusive  option for six (6) months  from the earlier of (A) the date that
notice  of  the  Separation  is  given  to the  Corporation  and  the  Remaining
Shareholders by the selling Shareholder or his  representative,  or (B) the date
that the Corporation notifies the selling Shareholder or his representative that
the Corporation is taking note of the occurrence of the event of Separation,  to
purchase all (but not less than all, except in the event of Separation resulting
from  Termination  For  Cause)  of the  selling  Shareholder's  Shares  in  such
proportion as the Corporation and the Remaining Shareholders shall agree. If the
Corporation  and the  Remaining  Shareholders  are unable to so agree,  then the
opportunity  to exercise the option shall be allocated and conducted in the same
manner  as is set forth in  Section  5(a)(i)  above  (including  the  provisions
thereof relating to Bernstein) as if the Remaining  Shareholders  were Surviving
Shareholders.

                   (ii) If the  Corporation,  and/or the Remaining  Shareholders
fail to tender at the  Closing (as that term is defined  below in Section  5(e))
the purchase price for all the Shares of the selling Shareholder pursuant to the
terms provided in Section 5(d) (except in the case of  Termination  For Cause in
which event the option may be  exercised  in respect of any or all of the Shares
of the selling Shareholder),  the option of the Corporation and/or the Remaining
Shareholders  to purchase  the selling  Shareholder's  Shares as a result of the
particular  event of Separation  described in the selling  Shareholder's  notice
shall

                                      -12

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expire.  However, the selling  Shareholder's Shares shall continue to be subject
to the right of first refusal set forth in Section 6 of this Agreement.

          (c)  Exercise  of  Option in the Event of  Separation  Resulting  From
Termination  For Cause.  In the event of Termination  For Cause of a Shareholder
within one year of the effective date of this Agreement,  the Corporation  shall
have the exclusive  option for six (6) months from the date of such  termination
to purchase all of the terminated Shareholder's shares on the terms set forth in
Section 5(d) below. In the event of Termination For Cause of a Shareholder  more
than one  year,  but less  than two  years,  after  the  effective  date of this
Agreement,  the  Corporation  shall have the exclusive  option to purchase fifty
percent (50%) of the terminated  Shareholder's  shares on the terms set forth in
Section 5(d) below, and the remaining fifty percent (50%) of such  Shareholder's
shares shall be subject to the option  described  in Section 5(b) above.  In the
event of  Termination  For Cause of a  Shareholder  more than two years from the
effective date of this Agreement, the Corporation and the Remaining Shareholders
shall  have  the  exclusive  option  for six (6)  months  from  the date of such
termination to purchase any or all of the terminated Shareholder's Shares in the
same manner and on the same terms as are set forth in Section 5(b) above.

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          (d)  Terms of  Payment.  In all  cases  other  than the  Corporation's
exclusive option to purchase all or half (as the case may be) of a Shareholder's
shares as a result of the  Termination  For Cause of a  Shareholder  within  two
years of the  effective  date hereof,  the selling  Shareholder  (or his estate)
shall be entitled to receive the Fair Market  Value Per Share of his Shares.  In
the event of Termination For Cause of a Shareholder  within two (2) years of the
effective date of this Agreement,  the selling  Shareholder shall have the right
to receive from the  Corporation  for those Shares subject to the  Corporation's
exclusive option set forth in Section 5(c) above, not more than the par value of
such  shares as adjusted  from time to time,  all to be paid in cash at one time
upon the  purchase  of such  shares  by the  Corporation.  Except  as  otherwise
provided in  subsection  (a) hereof,  the terms of payment for Shares  purchased
pursuant to subsection (a) and (b) of this Section 5 shall be as follows:

                     (i) Each purchaser shall make a down payment of ten percent
(10%) of the total purchase price of the Shares  purchased by him (not to exceed
One Hundred Thousand ($100,000) Dollars) at the time such Shares are surrendered
(the "Closing"),  and shall simultaneously deliver to the selling Shareholder or
his representative, as the case may be, a negotiable note (the "Note") signed by
the purchaser and payable to the order of the selling Shareholder,  in an amount
equal to the balance of the purchase price of such Shares.  Notwithstanding  the
foregoing,

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to the extent that payment is made out of the proceeds of any applicable key man
insurance  policy  maintained  by  the  Corporation,  the  down  payment  by the
Corporation  shall be not less than the net proceeds of such  policy,  up to the
full amount of the  purchase  price,  and the  Closing  shall be  postponed,  if
necessary,  until such proceeds are received.  Any purchaser  may, in his or its
sole discretion,  increase the amount of his down payment to any amount,  or pay
the entire purchase price at the Closing.

                     (ii) The Note  shall be due and  payable  in not more  than
five (5) equal annual principal  installments,  beginning one (1) year after the
date of the Note.  Interest shall accrue on the unpaid balance of the Note at an
annual  rate equal to the  applicable  federal  rate under  Section  1274 of the
Internal  Revenue Code of 1986,  as amended (or any  successor  provision),  and
shall be  payable  quarterly  beginning  on the  first day of the  fourth  month
following  the date of the Note.  If the  purchaser  fails to pay any amount due
under the Note within thirty (30) days after  written  notice of such default is
given to such purchaser,  the selling  Shareholder  shall have the right, at his
sole  option,  to declare  the entire  unpaid  balance,  together  with  accrued
interest,  immediately  due and  payable.  In the event of default,  the selling
Shareholder  shall also be entitled to collect all reasonable fees and expenses,
including,  but not limited to, reasonable attorneys' fees incurred in enforcing
his rights under the Note. Each such Note shall also provide that the

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purchaser may pre-pay the whole or any part of the remaining  principal  balance
at any time without notice or penalty.

                     (iii) In  conjunction  with the  delivery of the Note,  the
purchaser  shall  execute  and  deliver to the  selling  Shareholder  a security
agreement,   in  a  form  mutually  acceptable  to  the  purchaser  and  selling
Shareholder,  granting to the  selling  Shareholder  a security  interest in the
purchased Shares as security for the Note and providing for the purchased Shares
to be held by an agent designated by the selling  Shareholder  until the Note is
paid in  full.  The  security  agreement  shall  prohibit  any  further  sale or
assignment of the Shares by the purchaser except a sale or assignment that would
result in payment  in full of the Note.  The  purchaser  shall have the right to
exercise all  incidents of  ownership,  including  the right to vote the Shares,
unless the  purchaser is in default  under the Note or the  security  agreement.
Remedies  upon any  default  under the Note shall be as  provided by the Uniform
Commercial Code as enacted in the State of Delaware.

               (e) Delivery of Shares.

                     (i) The  Closing  shall  take place  within sixty (60) days
after  determination  of the Fair Market Value Per Share (or, in the case of the
Corporation's  option to purchase at par value  pursuant to Section  (5)(c),  on
such date as shall be determined  by the Board of Directors of the  Corporation,
but not more





                                      -16-
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than six (6) months following the effective date of Termination For Cause), at a
time  and  place  mutually   agreeable  to  the  selling   Shareholder  and  the
purchaser(s).   If  there  is  more  than  one  purchaser  of  the  Shares,  the
consummation  of the  purchases  shall  take place at a single  closing,  to the
extent  reasonably  practicable.  The  Closing  shall be  extended to the extent
reasonably  necessary if the event of Separation  (for example,  death) requires
the appointment of a representative for the Shareholder and such  representative
is unable to effectuate such sale within such sixty-day period.

                     (ii) At the Closing,  the selling Shareholder shall deliver
the Shares to be sold to the  purchaser  or the agent,  as required  pursuant to
subsection  (d)(iii)  of this  Section  5,  free  and  clear  of all  liens  and
encumbrances.  The Shares shall be duly  endorsed for transfer to the  purchaser
and shall be accompanied  by all other documents  necessary for their effective
immediate transfer to the purchaser.

                     (iii) Simultaneously with delivery, the purchaser shall pay
the  purchase  price of the Shares in  accordance  with  subsection  (d) of this
Section 5.

               6. Right of First Refusal.

                     (a) Grant of Right.  No Shareholder  shall sell,  assign or
otherwise transfer all or any portion of his Shares to a

                                      -17-

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person who is not a Shareholder  without giving the other  Shareholders  and the
Corporation  a right of first  refusal to purchase such Shares in the manner set
forth in this Section 6.

                     (b)  Purchase by the  Corporation  and Other  Shareholders.
Upon  receiving an offer to purchase any such  Shares,  the selling  Shareholder
shall  require the  offeror to submit a Bona Fide Offer  which such  Shareholder
then shall transmit to the  Corporation and the other  Shareholders  (the "Other
Shareholders"). The Corporation and the Other Shareholders shall have sixty (60)
days  thereafter  in which to purchase all (but not less than all) of the Shares
referred to in the Bona Fide Offer at the same price and terms  contained in the
Bona Fide Offer.  If any or all of the Other  Shareholders  are  exercising  the
right of first refusal hereunder,  each of them shall have the priority right to
purchase  such Shares in such  proportion as the total number of Shares owned by
each  participating  Other  Shareholder shall bear to the total number of Shares
then owned by all participating Other Shareholders; and any of the Shares not so
subscribed for by each participating Other Shareholder shall be allocated in one
or more successive  allocations to those Other Shareholders who wish to purchase
additional  Shares and each such  allocation  shall be determined by a fraction,
the  numerator  of which is the  number  of  shares  owned  by each  such  Other
Shareholder  and the  denominator  of which is the number of Shares owned by all
such Other Shareholders. Bernstein shall not be considered an Other

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Shareholder  for purposes  hereof  unless he shall have first  converted his RPC
into Shares pursuant to the terms thereof; provided, however, that if not all of
the selling  Shareholder's  Shares would be purchased pursuant to the provisions
hereof,  then at the Corporation's  option in its sole discretion  Bernstein may
elect to purchase any such remaining  Shares.  To the extent that the purchasers
fail to tender the full cash purchase price (or to match such other terms as are
contained in the Bona Fide Offer) for all of the Shares  referred to in the Bona
Fide Offer  against the proper  endorsement  and  delivery  of the  certificates
evidencing the Shares within such sixty-day period,  this right of first refusal
shall  expire as to that  particular  Bona Fide Offer,  but shall remain in full
force and effect with  respect to all material  modifications  of that Bona Fide
Offer and all future offers.

                     (c) Purchase by Third Party.  Any Offered  Shares which are
not purchased by the  Shareholders  or the Corporation as provided herein may be
sold to the person,  firm,  association  or  corporation  named in the Bona Fide
Offer,  but not at a lower price, or upon more favorable terms to the purchaser,
then the price and terms set forth in the Bona Fide Offer. Title to such Offered
Shares  shall pass not later than ninety (90) days from the latest date on which
the Other  Shareholders or the  Corporation  have declined or failed to purchase
the Shares. In the event that the selling Shareholder should desire to sell such
Shares at a lower price, or upon terms more favorable to the purchaser, than he

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theretofore offered the Shares to the Other Shareholders or the Corporation,  he
shall,  before he can sell to any such  purchaser,  again  offer  the  Shares in
accordance with the procedure set forth in this Section 6.

               7. Transfer to Family  Members.  Notwithstanding  anything to the
contrary contained herein, each Shareholder shall have the right to transfer all
or any of his  Shares  at any time by will or deed to one or more of his  Family
members  (hereinafter  called  "Close  Assigns").  However,  whenever  any  such
Shareholder  shall thus  dispose of Shares among his Close  Assigns,  such Close
Assigns  and the Shares  owned by them shall  continue to be bound by all of the
terms and conditions of this  Agreement.  Without  limiting the  foregoing,  the
option to purchase  granted in Section 5 and the right of first refusal  granted
in  Section  6 with  reference  to the  Shares  of  such  Shareholder  shall  be
applicable to the Shares of his Close Assigns as if such Shareholder still owned
such Shares.

               8. Transferees of Shares.  Any transferee of Shares (other than a
Close Assign of a Shareholder  as defined in Section 7) who is not a Shareholder
must execute a written  consent to be bound by this Agreement to the same extent
as a Shareholder.  Any such transferee shall be considered a Shareholder for all
purposes  under  this  Agreement;  except  that  no  such  transferee  shall  be
considered a Shareholder whose Shares are subject to the purchase

                                      -20-

<PAGE>
option contained in Section 5 unless such transferee is, or becomes,  engaged by
the Corporation in a managerial or advisory capacity.

         9. Agreement by Corporation.  The Corporation agrees for itself and its
successors and assigns that (i) insofar as is proper or required, it consents to
this Agreement;  (ii) it will not transfer or reissue any Shares in violation of
this  Agreement,  or without  requiring proof of compliance with this Agreement;
and (iii) all other actions required of the Corporation pursuant to the terms of
this Agreement shall be promptly and faithfully performed.

         10.  Departing  Shareholders.  Upon the sale or other  disposition by a
Shareholder  of the  beneficial  ownership  of all of his  Shares,  the  selling
Shareholder  shall  no  longer  be  deemed  to be  either  a party  hereto  or a
"Shareholder"  hereunder,  and shall have no further rights or obligations under
this  Agreement,  except that he shall remain liable to the other parties hereto
for all violations of this  Agreement  committed by him in  connection  with the
disposition of his Shares.

         11. Failure to Surrender  Shares. If a Shareholder or any person having
custody or control of his Shares  fails or refuses to tender  such  Shares as is
required  by the terms of this  Agreement,  all right to vote such  Shares or to
receive dividends or other  distributions with respect thereto shall cease as of
the

                                       21
<PAGE>

time such  Shares  should  have been  surrendered.  The only rights of the owner
thereof  shall be to collect and receive the  purchase  price per Share as above
provided,  and no interest  shall accrue thereon as a result of any delay in the
surrender of such Shares.

         12. Conversion of Non-Voting Shares to Voting Shares. In the event that
Titomirov or the  Corporation  has entered into an agreement or has undertaken a
course of action that results or would result in Titomirov owning or potentially
owning less than fifty-one percent (51%) of the outstanding voting shares of any
class  of the  Corporation,  then,  without  further  action  or  payment by any
Shareholder,  the Corporation shall immediately offer in writing to exchange any
and all  non-voting  Shares held by any  Shareholder  or Close Assign for voting
Shares of the Corporation.  The Corporation and the  Shareholders  agree to take
any action necessary or appropriate to give effect to this provision, including,
but not  limited  to, the taking of any  corporate  actions,  the  execution  of
consents,  the  holding  of  meetings  of  directors  or  shareholders  and  the
preparation, execution and filing or delivery of any  certificates,  as and when
required,  and, in any event,  prior to  Titomirov's  owning less than fifty-one
(51%) of the Corporation's outstanding voting Shares of any class.


                                       22
<PAGE>

     13. Proprietary Information.

         (a) Definitions. The parties acknowledge that each will be furnished or
may  otherwise  receive  or have  access to  information  which  relates  to the
Corporation's past, present or future products, software, research, development,
improvements,  processes, techniques, design or other technical data, customers,
suppliers,  contractors, or regarding administrative,  management, financial, or
marketing activities, or of a third party which provided proprietary information
to one  or  more  of the  parties  hereto  on a  confidential  basis.  All  such
information,  including any materials or documents  containing such information,
are  proprietary  and  confidential  to the disclosing  party (the  "Proprietary
Information").


         (b) Nondisclosure.  Both  during and after the term of this  Agreement,
each party agrees to preserve  and protect the  confidentiality  of  Proprietary
Information  and all  physical  forms  thereof,  whether  disclosed  before this
agreement is signed or afterward.  In addition,  the  receiving  party shall not
disclose or distribute any Proprietary Information to any third party, and shall
not use any  Proprietary  Information  for  his or its  own  benefit  or for the
benefit  of any third  party.  The  foregoing  obligations  shall not apply with
respect to any  Proprietary  Information  the disclosing  party can establish to
have become publicly known without breach of this Agreement.

                                       23
<PAGE>


     (c)  Return of  Proprietary  Information.  Each party  shall  return to the
Corporation  all documents and other  tangibles,  including  diskettes and other
storage media (and  all copies and  reproductions of any of the foregoing) which
contain any Proprietary Information immediately upon request by the Corporation.

         14.  Competition.  During  the term  thereof,  or for a period of three
years  following an Event of Separation of a Shareholder,  or at any time within
two years following the date that a Shareholder no longer owns any Shares,  such
party  will  not,  and such  party  shall  use his  best  efforts  to cause  his
employees,  agents and  affiliates  not to (i) own any interest in,  provide any
financing for or perform any services for, any business or entity which engages,
directly or indirectly,  in  competition in any respect with the  Corporation or
(ii) engage in competition with the Corporation.  Each party further agrees that
during such  period he will not  solicit  any current or former  customer of the
Corporation,  or solicit or employ any current employee of the  Corporation,  or
any contractor of the Corporation providing software  development,  modification
or enhancement services to or for the Corporation.

         15.  Remedies  for  Breach of  Agreement.  Each  Shareholder  agrees as
follows:

              (a) that any breach or attempted  breach by him of the  provisions
of this Agreement could result in irreparable injury



                                       24
<PAGE>

to any or all of the other  parties  hereto for which there would be no adequate
remedy at law;

     (b) that if he should  breach or attempt to breach any such  provisions  of
this  Agreement,  one or  more of the  other  parties  hereto  who are or may be
injured by such breach or attempted  breach may seek  through  process of law to
enjoin him from further breaches or attempted  breaches hereof, or to compel his
compliance  with such  provisions  by specific  performance,  in addition to any
other remedies available in equity or at law; and

     (c)  that if a  court  of  competent  jurisdicition  determines that he has
breached,  or attempted to breach,  any such  provisions of this  Agreement,  he
shall pay all costs and expenses, including, without limitation, court costs and
the reasonable  attorneys' fees,  incurred by the other parties in enforcing his
obligations under this Agreement.

         16.  Notices.  Any and all  notices,  consents or other  communications
provided for herein shall be given in writing and  personally  delivered or sent
by telex,  telecopy,  telegram or other overnight mail with appropriate evidence
of  transmission  or receipt,  or by registered by certified  mail  addressed as
follows:  (i) if to the  Corporation,  to its current office address at the time
such notice,  consent or other  communication  is to be given,  and (ii) if to a
Shareholder,  to  his  most  recent  address  appearing  on the  records  of the
Corporation. Each such notice, consent or


                                       25
<PAGE>
other communication shall be deemed given on the date it is personally delivered
of, if mailed, on the date of mailing.

         17.  Severability.  The  provisions  of this  Agreement shall be deemed
severable,  and the  invalidity or  unenforceability of any  provision shall not
affect the validity or  enforceability of the remainder of this Agreement or any
valid clause of an invalid provision.

         18. Entire Agreement.  This Agreement contains the entire agreement and
understanding  among the parties  hereto with  respect to the matters  contained
herein  and may not be  modified  except  by a written  agreement  signed by the
Corporation  and all of the  other  parties  to  this  Agreement  who  are  then
shareholders of the Corporation.  This Agreement supersedes all prior agreements
or  understandings,  oral or written,  among the parties relating to the subject
matter hereof.

         19.  Corporate  Authorization.  The proper  officers of the Corporation
have been  authorized to enter into this Agreement on behalf of the  Corporation
by a resolution adopted by its board of directors.

         20.  Governing Law;  Consent to  Jurisdiction.  This Agreement shall be
construed  under and  governed in all  respects,  including  issues of validity,
interpretation,  performance  and  enforcement,  by the  laws  of  the  District
Columbia. Each of the parties

                                       26
<PAGE>


hereby  irrevocably  consents to, and waives any  objections to the exercise of,
personal  jurisdiction by the courts in the District of Columbia with respect to
any action or proceeding arising out of this Agreement.


         21. Binding Effect. This Agreement shall inure to the benefit of and be
binding  upon the  Corporation  and its  successors  and  assigns  and upon each
Shareholder and his heirs, legatees,  personal  representatives and assigns, but
neither this Agreement nor any right or obligation hereunder shall be assignable
by any party  without the express  written  consent of all of the other  parties
hereto.

         IN WITNESS  WHEREOF,  the parties have signed this  Agreement as of the
date first written above.

ATTEST:

WITNESSES:                                 Shareholders:


/s/   C. Bowdoin Train                     /s/ Alexander Titomirov
-------------------------------            --------------------------------
                                           Alexander Titomirov

/s/   Alexander Titomirov                  /s/ Valera Sagitov
-------------------------------            --------------------------------
                                           Valera Sagitov

/s/   Alexander Titomirov                  /s/ James E. Bernstein
-------------------------------            --------------------------------
                                           James E. Bernstein


                                       27

<PAGE>
/s/    Alexander Titomirov                 /s/ C. Bowdoin Train
-------------------------------            --------------------------------
                                            C. Bowdoin Train

/s/    Alexander Titomirov                 /s/ Louis Hecht
-------------------------------            --------------------------------
                                           Louis Hecht

/s/    Alexander Titomirov                 /s/ Brennan Klose
-------------------------------            --------------------------------
                                           Brennan Klose


                                           The Corporation:

                                           INFORMAX, INC.

/s/ Peter Van Story                        /s/ Alexander Titomirov
--------------------------------           --------------------------------
Peter Van Story                            Alexander Titomirov
Secretary                                  President




                                       28
<PAGE>



                                 FIRST AMENDMENT
                         TO THE SHAREHOLDERS' AGREEMENT

         THIS FIRST AMENDMENT TO THE  SHAREHOLDERS'  AGREEMENT (the "AMENDMENT")
is made as of 17 August 1999, by and among  Alexander  Titomirov  ("TITOMIROV"),
James  E.  Bernstein   ("BERNSTEIN"),   C.  Bowdoin  Train,  and  Brennan  Klose
(collectively,  the  "CURRENT  SHAREHOLDERS")  and  InforMax,  Inc.,  a Delaware
corporation (the "CORPORATION").

         WHEREAS,   the  Current   Shareholders  are  parties  to  that  certain
Shareholders'  Agreement by and among Valera Sagitov ("SAGITOV") and Louis Hecht
(together with Sagitov, the "FORMER  SHAREHOLDERS"),  the Current  Shareholders,
and the  Corporation  dated as of  September  1, 1990,  as amended  hereby  (the
"SHAREHOLDERS' AGREEMENT");

         WHEREAS,  the  Former  Shareholders  each  ceased  to be a party to the
Shareholders'  Agreement upon the disposition of all of their respective  shares
of the Corporation's common stock;

         WHEREAS,  the  Corporation and FBR Technology  Venture  Partners II, LP
("FBR")  entered into that certain Series A Preferred  Stock Purchase  Agreement
("SERIES A  PREFERRED  STOCK  PURCHASE  AGREEMENT")  dated as of June 22,  1999,
pursuant to which among other things FBR: (a) made an equity investment into the
Corporation,  and (b) entered into that certain  Investor Rights Agreement dated
as of June 22, 1999, by and between FBR and the  Corporation  (together with any
amendments thereto, the "INVESTOR RIGHTS AGREEMENT");

         WHEREAS, pursuant to the terms of the Series A Preferred Stock Purchase
Agreement:  (a)  Vadim  Babenko,  Bernstein  and  Titomirov  (collectively,  the
"FOUNDERS"),  FBR and the  Corporation  entered into that certain Right of First
Refusal and Co-Sale  Agreement,  dated as of June 22,  1999  (together  with any
amendments  thereto,  the "FIRST  REFUSAL AND CO-SALE  AGREEMENT");  and (b) the
Founders,  FBR and the  Corporation  entered into that certain Voting  Agreement
dated as of June 22, 1999  (together with any  amendments  thereto,  the "VOTING
AGREEMENT");

         WHEREAS,  the Current  Shareholders  are desirous of amending the terms
and conditions of the Shareholders' Agreement as set forth herein; and

         WHEREAS,  capitalized  terms used and not defined herein shall have the
meaning ascribed to such terms in the Shareholders' Agreement.

         NOW,  THEREFORE,  in  consideration  of the  above  and for the  mutual
covenants and  agreements  hereinafter  set forth,  the parties  hereto agree as
follows:

         1.       Matters Relating to Section 12.


<PAGE>

                  (a) The parties hereto acknowledge and agree that in the fifth
line of Section 12 of the Shareholders' Agreement the phrase "outstanding voting
shares" shall be corrected to read as follows, "outstanding voting Shares".

                  (b) The parties hereto  acknowledge  and agree that in Section
12 of the  Shareholders'  Agreement the provisions  regarding the  circumstances
pursuant to which nonvoting common stock is automatically  converted into voting
common stock shall only apply when Titomirov no longer has voting control of the
Corporation.

         2.  Amendment  to Section 3. Section 3 of the  Shareholders'  Agreement
shall be amended to add as the last sentence of Section 3, the following:

                   Notwithstanding  anything to the contrary  herein,  including
         this  Section 3, each  Shareholder  shall take all action  necessary in
         order to carry out the intents and purposes of the Voting Agreement.

         3.  Amendment  to Section 5. Section 5 of the  Shareholders'  Agreement
shall be amended to add a new subsection (f) which shall read in its entirety as
follows:

                   (f)   Notwithstanding   anything  to  the  contrary   herein,
         including  this  Section  5,  each   Shareholder  and  the  Corporation
         acknowledges  and agrees  that any rights of first  refusal  granted to
         such  Shareholders or the Corporation,  as the case may be, pursuant to
         this  Section 5, shall be  subject to the rights of first  refusal  and
         co-sale  granted  to FBR  pursuant  to the  terms of the Right of First
         Refusal and Co-Sale  Agreement as set forth and limited by the terms of
         such Right of First Refusal and Co-Sale Agreement.

         4.  Amendment  to Section 7. Section 7 of the  Shareholders'  Agreement
shall be amended to add as the last sentence to Section 7, the following:

                   Notwithstanding  anything to the contrary  herein,  including
         this  Section 7, each Founder  acknowledges  and agrees that any rights
         conferred  upon such  Founder  pursuant  to this  Section  7,  shall be
         exercised by such Founder in a manner  consistent  with the limitations
         on such rights provided for in the First Refusal and Co-Sale Agreement.

         5. Amendment to Section 14. Section 14 of the  Shareholders'  Agreement
is hereby amended in its entirety to read as follows:

                  14.      Noncompetition.

                           (a) Covenants.  During the term of this Agreement and
         for a period  of twenty  four (24)  months  after  termination  of this
         Agreement (the "Noncompetition Period"), no Shareholder shall, directly
         or indirectly, as an officer, director,  employee,  consultant,  owner,
         shareholder,  adviser,  joint venturer, or otherwise,  compete with the
         Company Business. This covenant

                                       2
<PAGE>

         shall not preclude a Shareholder from owning less than two percent (2%)
         of  the  securities  of  any  competitor  of the  Corporation  if  such
         securities  are  publicly  traded  on  a  nationally  recognized  stock
         exchange or  over-the-counter  market. For purposes of this Section 14,
         the term "Company  Business"  shall mean the business of developing and
         licensing pharma-informatic software tools of the type developed by the
         Corporation.

                           (b)  Acknowledgments.  Each Shareholder  acknowledges
         that the foregoing  restriction on competition is fair and  reasonable,
         given  the  scope  of the  Company  Business  and  the  nature  of such
         Shareholder's  relationship  with  the  Corporation.  Each  Shareholder
         acknowledges  that such  Shareholder has had, and will have,  access to
         information  that  would be  valuable  or useful  to the  Corporation's
         competitors, and therefore acknowledges that the foregoing restrictions
         on such  Shareholders'  future  employment and business  activities are
         fair and reasonable.  Each Shareholder acknowledges and is prepared for
         the  possibility  that such  Shareholder's  standard  of living  may be
         reduced during the  Noncompetition  Period, and assumes and accepts any
         risk associated with that possibility.

         6. Waiver of Rights. Each Shareholder and the Corporation  acknowledges
and  agrees  that  this  Amendment  constitutes  a  waiver  of any  rights  such
Shareholder or the  Corporation has pursuant to the  Shareholders'  Agreement to
the extent any such rights are  inconsistent  with the First Refusal and Co-Sale
Agreement, the Investor Rights Agreement or the Voting Agreement.

         7.  Scope of  Amendment.  Except  as  expressly  modified  hereby,  the
Shareholders'  Agreement is hereby  ratified and confirmed and shall continue in
full force and effect.



             [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]


                                       3
<PAGE>


         IN  WITNESS  WHEREOF,  each of the  parties  hereto has  executed  this
Amendment to the  Shareholders'  Agreement  or has caused this  Amendment to the
Shareholders'  Agreement to be duly  executed  and  delivered in its name on its
behalf, all as of the day and year first written above.

CURRENT SHAREHOLDERS:

/s/ Alexander Titomirov                   /s/ C. Bowdoin Train
------------------------------            ---------------------------------
Alexander Titomirov                       C. Bowdoin Train

/s/ James E. Bernstein
------------------------------            ---------------------------------
James E. Bernstein                        Brennan Klose


                                          THE CORPORATION: INFORMAX, INC.

                                          /s/ Alexander Titomirov
                                          ---------------------------------
                                          Alexander Titomirov
                                          President and Chief Executive Officer


                                       4
<PAGE>

                                 SECOND AMENDMENT

                         TO THE SHAREHOLDERS' AGREEMENT

     THIS SECOND AMENDMENT TO THE  SHAREHOLDERS'  AGREEMENT (the "AMENDMENT") is
made as of March 29, 2000, by and among Alexander Titomirov ("TITOMIROV"), James
E. Bernstein ("BERNSTEIN"),  C. Bowdoin Train ("TRAIN"), Brennan Klose ("KLOSE";
collectively  with Titomirov,  Bernstein and Train, the "CURRENT  SHAREHOLDERS")
and InforMax,  Inc., a Delaware corporation (the "CORPORATION") and WPG Software
Fund, L.P., WPG Raytheon Software Fund, L.P., WPG  Institutional  Software Fund,
L.P.,  WPG  Networking  Fund,  L.P.,  WPG Raytheon  Networking  Fund,  L.P., WPG
Institutional Networking Fund, L.P., and Raj Mehra (the "BUYERS").

         WHEREAS,   the  Current   Shareholders  are  parties  to  that  certain
Shareholders'  Agreement by and among Valera Sagitov ("Sagitov") and Louis Hecht
(together with Sagitov, the "FORMER  SHAREHOLDERS"),  the Current  Shareholders,
and the  Corporation  dated as of  September  1, 1990,  as amended  hereby  (the
"SHAREHOLDERS' AGREEMENT");

         WHEREAS,  the  Former  Shareholders  each  ceased  to be a party to the
Shareholders'  Agreement upon the disposition of all of their respective  shares
of the Corporation's common stock;

         WHEREAS,  the Current  Shareholders,  FBR  Technology  Venture  Capital
Managers, Inc. ("FBR") and the Corporation entered into that certain Side Letter
Agreement,  dated June 22, 1999, pursuant to which the Current  Shareholders and
the   Corporation   subordinated   their  rights  of  first  refusal  under  the
Shareholders'  Agreement  regarding transfers of Shares to the rights granted to
FBR pursuant to that certain Right of First Refusal and Co-Sale  Agreement dated
as June 22, 1999, by and among FBR, the  Corporation,  the Current  Shareholders
and Vadim Babenko ("BABENKO");

         WHEREAS, Titomirov and Babenko and the Buyers entered into that certain
Stock Purchase  Agreement  ("STOCK  PURCHASE  Agreement")  dated as of March 29,
2000,  pursuant to which,  among other  things,  (a)  Titomirov and Babenko have
exercised  options (the  "OPTIONS") to purchase in the aggregate  750,000 shares
from the Corporation  (the "OPTION  SHARES") for an aggregate  purchase price of
Three  Hundred  Seventy-Five  Thousand  Dollars  ($375,000);   (b)  Babenko  and
Titomirov  exercised the Options on the  understanding  that the Corporation and
the other  Current  Shareholders  would  enter into this  Amendment;  (c) Buyers
entered  into  the  Stock  Purchase  Agreement  on the  understanding  that  the
Corporation and the other Current Shareholders would enter into this Amendment;

         WHEREAS,  the Buyers and the Current  Shareholders  are desirous of the
Buyers joining the Shareholder's Agreement for purposes Section 6 and Section 12
of the Shareholders' Agreement only;

         WHEREAS,  the Current  Shareholders  are desirous of amending the terms
and conditions of the Shareholders' Agreement as set forth herein;

<PAGE>
         WHEREAS,  the parties have agreed that Buyers' right  hereunder will be
subordinate to the rights of FBR under the First Refusal and Co-Sale  Agreement;
and

         WHEREAS,  capitalized  terms used but not defined herein shall have the
meaning ascribed to such terms in the Shareholders' Agreement.

         NOW,  THEREFORE,  in  consideration  of the  above  and for the  mutual
covenants and  agreements  hereinafter  set forth,  the parties  hereto agree as
follows:

         1.       Matters Relating to Section 6.
                  -----------------------------

                  (a) The parties hereto  acknowledge  and agree that the Buyers
are a party to the  Shareholder's  Agreement  for all purposes of Section 6, and
shall be a  "Shareholder"  for purposes of Section 6, and that the first line of
Section  6(a) of the  Shareholders'  Agreement  shall be  amended to read in its
entirety as follows:

                   Except for the Buyers,  no Shareholder  shall sell, assign or
otherwise  transfer  all or any  portion  of his Shares to a person who is not a
Shareholder without giving the other Shareholders, including the Buyers, and the
Corporation  a right of first  refusal to purchase such Shares in the manner set
forth in this Section 6.

                  (b) The parties  hereto  acknowledge  and agree that the first
line of Section 6(b) of the  Shareholders'  Agreement shall be corrected to read
as follows:

                  Upon  receiving  an offer to  purchase  any such  Shares,  the
selling  Shareholder shall require the offeror to submit a Bona Fide Offer which
such   Shareholder  then  shall  transmit  to  the  Corporation  and  the  Other
Shareholders, including the Buyers (the "Other Shareholders").

                  (c)  The  parties  hereto   acknowledge  and  agree  that  all
remaining  provisions  of Section 6 of the  Shareholders'  Agreement  are hereby
ratified and confirmed and shall continue in full force and effect.

         2.       Matters Relating to Section 12.

                  (a) The parties hereto  acknowledge  and agree that the Buyers
are a party to the  Shareholder's  Agreement  for purposes of all of Section 12,
and shall be a "Shareholder" for purposes of Section 12, and that the first line
of Section  12 of the  Shareholders'  Agreement  shall be amended to read in its
entirety as follows:

                  In the event  Titomirov or the Corporation has entered into an
agreement  or has  undertaken a course of action that results or would result in
Titomirov owning or potentially  owning less than fifty-one percent (51%) of the
outstanding  voting Shares of the Corporation,  then,  without further action or
payment  by  any  Shareholder,  including  the  Buyers,  the  Corporation  shall
immediately  offer in writing to exchange any and all non-voting  Shares held by
any Shareholder,  including the Buyers, or Close Assign for voting Shares of the
Corporation.

                                       2
<PAGE>

                  (b)  The  parties  hereto   acknowledge  and  agree  that  all
remaining  provisions  of Section 12 of the  Shareholders'  Agreement are hereby
ratified and confirmed and shall continue in full force and effect.

         3.  Scope of  Amendment.  Except  as  expressly  modified  hereby,  the
Shareholders'  Agreement is hereby  ratified and confirmed and shall continue in
full force and effect.

         4.  Joinder to Side  Letter.  (a) The Buyers are hereby made a party to
the Side Letter as a "Principal Shareholder"  thereunder,  and the Buyers hereby
agree  to be bound by all the  terms  and  conditions  of the Side  Letter  as a
"Principal Shareholder" thereunder.

                  (b)  The  Buyers  represent  and  warrant individually  to the
Company and the other Principal  Shareholders  and FBR that each Buyer:  (a) has
reviewed  the Side  Letter  (as  attached  hereto),  and fully  understands  all
provisions of the Side Letter, and (b) has become a Principal  Shareholder under
the Side Letter and is bound by all the terms and  conditions of the Side Letter
with the same  effect as though  the Buyer was a  subscribing  party to the Side
Letter.

                  (c)  All   references   in  the  Side  Letter  to   "Principal
Shareholder" or "Principal Shareholders" shall be deemed to include the Buyer.

                  (d) Except as provided herein, all of the terms and conditions
of the Side Letter are  unmodified  and shall  continue in full force and effect
and shall be binding  upon the parties  hereto and their  respective  assigns in
accordance with the terms thereof.

         5.  Counterparts.   This  Amendment  may  be  executed   (including  by
facsimile)  in one or more  counterparts,  each of  which  shall  be  deemed  an
original but all of which together will constitute one and the same instrument.


              [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]



                                       3
<PAGE>

                  IN WITNESS  WHEREOF,  each of the parties  hereto has executed
this First  Amendment  to the  Shareholders'  Agreement or has caused this First
Amendment to the  Shareholders'  Agreement to be duly  executed and delivered in
its name on its behalf, all as of the day and year first written above.

CURRENT SHAREHOLDERS:

/s/ Alexander Titomirov                       /s/ C. Bowdoin Train
-----------------------------                 ----------------------------------
Alexander Titomirov                           C. Bowdoin Train

/s/ James E. Bernstein
-----------------------------                 ----------------------------------
James E. Bernstein                            Brennan Klose


                                              THE CORPORATION:

                                              INFORMAX, INC.

                                              By: /s/ Joe Lehnen
                                                  ------------------------------
                                                  Joe Lehnen
                                                  Chief Financial Officer

                                              BUYERS:

                                              WPG SOFTWARE FUND, L.P.,
                                              BY ITS GENERAL PARTNER

                                              By: /s/ Benjamin Taylor BT/RM
                                                  ------------------------------
                                                  Benjamin Taylor, in his
                                                  individual capacity


                                              WPG RAYTHEON SOFTWARE FUND,
                                              L.P., BY ITS GENERAL PARTNER


                                              By:  /s/ Benjamin Taylor BT/RM
                                                   -----------------------------
                                                   Benjamin Taylor, in his
                                                   individual capacity



<PAGE>

                                              WPG INSTITUTIONAL SOFTWARE
                                              FUND, L.P., BY ITS GENERAL PARTNER


                                              By: /s/ Benjamin Taylor BT/RM
                                                  ------------------------------
                                                  Benjamin Taylor, in his
                                                  individual capacity


                                              WPG NETWORKING FUND, L.P., BY ITS
                                              GENERAL PARTNER


                                              By: /s/ Raj Mehra
                                                  -----------------------------
                                                  Raj Mehra, in his
                                                  individual capacity


                                              WPG RAYTHEON NETWORKING
                                              FUND, L.P., BY ITS GENERAL PARTNER


                                              By: /s/ Raj Mehra
                                                  -----------------------------
                                                  Raj Mehra, in his
                                                  individual capacity


                                              WPG INSTITUTIONAL NETWORKING
                                              FUND, L.P., BY ITS GENERAL PARTNER


                                              By: /s/ Raj Mehra
                                                  -----------------------------
                                                  Raj Mehra, in his
                                                  individual capacity


                                              RAJ MEHRA

                                              By: /s/ Raj Mehra
                                                  ------------------------------