Document:

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                                                                   EXHIBIT 10.28

                                February 14, 2002

John Green
4101 Fordham Road, NW
Washington, DC 20016

Re: Letter Agreement Concerning Severance

Dear John:

        As a corporate retention strategy, InforMax, Inc. ("InforMax" or the
"Company") agrees to provide you with certain additional severance benefits
under the terms and conditions set forth herein.

        In consideration of the promises of the parties to this Letter
Agreement, the receipt and sufficiency of which are hereby acknowledged, the
parties agree to amend the Employment Agreement by and between you and the
Company dated as of February 28, 2001 (the "Employment Agreement") as follows:

        The parties agree that Section 4(c) of the Employment Agreement,
captioned "Termination of Employment," "Termination Without Cause other than
upon a Change of Control," shall be amended to state:

                (c) Termination without Cause other than upon a Change of
                Control. InforMax shall pay Employee a lump-sum cash payment in
                an amount equal to one-hundred percent (100%) of Employee's
                annual base salary, plus an additional pro rata bonus payment
                not to exceed fifty percent (50%) of Employee's annual base
                salary, for the previous twelve (12) months upon termination by
                InforMax of Employee's employment without cause other than as
                provided in Section 4(b) above. The amount of such additional
                bonus payment shall be calculated by multiplying (x) fifty
                percent (50%) of Employee's annual base salary, by (y) such
                fraction, the numerator of which equals the number of completed
                months of Employee's employment in the calendar year in which
                the Employee was terminated by the Company under this
                subsection, and the denominator of which equals twelve (12). The
                severance payment shall be paid to Employee in cash as promptly
                as practicable, but in no event later than thirty (30) days
                following the termination of his employment. The employee shall
                have 30 days from the date of termination to exercise all vested
                options. Employee's options will cease vesting on the date of
                termination.

The parties also agree that Section 4(e), currently captioned "Termination of
Employment," "Voluntary Termination by Employee without Cause," shall be amended
to state:

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                (e) Voluntary Termination by Employee without Cause or for other
                than Good Reason. Any termination of Employee's employment by
                resignation, retirement or any other action of Employee for any
                reason other than as set forth in Section 4(d) or Section 4(g)
                below shall be deemed to be a "Voluntary Termination." Employee
                shall give InforMax thirty (30) days notice of a Voluntary
                Termination.

        The parties also agree that Section 4, captioned "Termination of
Employment," shall be amended to include a new subsection (g) "Termination by
Employee for Good Reason":

                (g) Termination by Employee for Good Reason. InforMax shall pay
                Employee a lump-sum cash payment in an amount equal to
                one-hundred percent (100%) of Employee's annual base salary,
                plus an additional pro rata bonus payment not to exceed fifty
                percent (50%) of Employee's annual base salary, for the previous
                twelve (12) months upon termination of employment by Employee
                for "Good Reason" (as defined below). The amount of such
                additional bonus payment shall be calculated by multiplying (x)
                fifty percent (50%) of Employee's annual base salary, by (y)
                such fraction, the numerator of which equals the number of
                completed months of Employee's employment in the calendar year
                in which the Employee terminates his employment for Good Reason,
                and the denominator of which equals twelve (12). For purposes of
                this subsection, the term "Good Reason" means (i) a change in
                Employee's position with the Company which materially reduces
                Employee's duties and responsibilities or the level of
                management to which Employee reports, (ii) a material reduction
                in Employee's level of compensation (including base salary,
                fringe benefits and target bonus under any corporate performance
                based bonus or incentive programs), or (iii) a relocation of
                Employee's place of employment by more than fifty (50) miles,
                provided and only if such change, reduction or relocation is
                effected by the Company without Employee's consent. The
                severance payment shall be paid to Employee in cash as promptly
                as practicable, but in no event later than thirty (30) days
                following the termination of his employment. The employee shall
                have 30 days from the date of termination to exercise all vested
                options. Employee's options will cease vesting on the date of
                termination.

        The parties also agree that the relevant option grant agreements in
connection with Employee's grant of 300,000 options on April 10, 2001 and
150,000 options on January 25, 2002 are hereby amended to provide Employee with
a period of up to 6 months from the date of his termination without "Cause" or
voluntary termination for "Good Reason," in which to exercise such options that
have vested and become exercisable prior to such employment termination date.
The option agreements governing the grants above shall otherwise remain
unchanged.

                                       2
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        Unless specifically modified herein, all terms and conditions of the
Employment Agreement and any other employment related agreements shall remain in
full force and effect and you agree that you will continue to be bound by such
agreements.

        This Letter Agreement may not be released or abandoned, supplemented or
modified in any manner, orally or otherwise, except by an instrument in writing
signed by each of the parties hereto. This Letter Agreement will be governed by
the laws of the State of Maryland and the parties agree to submit to the
exclusive jurisdiction of any Maryland court or Federal Court sitting in
Maryland in any action or proceeding arising out of or relating to this Letter
Agreement or the transactions contemplated hereby.

        Please evidence your understanding of and agreement with the
above-stated terms by signing below and returning this Letter Agreement to me.

                                    Yours sincerely,

                                    INFORMAX, INC.

                                    By:/S/ Alexander Titomirov, Ph.D.
                                       ------------------------------
                                    Alexander Titomirov, Ph.D.
                                    Chairman and Chief Executive Officer

AGREED:

/S/ John Green
-------------------------------
John Green
Chief Financial Officer and
Chief Operating Officer

February 18, 2002
-------------------------------
Date

                                       3<PAGE>

                                                                   EXHIBIT 10.29

                             [INFORMAX LETTERHEAD]

                            PRIVILEGED COMMUNICATION

Mr. Richard Melzer
1515 Gordon Cove Drive
Annapolis, MD  21403

April 8, 1999

Dear Richard:

We are very pleased that you have decided to join the InforMax team! This letter
conveys our understanding with you concerning your employment with InforMax.

1.  You will be employed as a Major Account Executive. You will be reporting to
    Jim Dickey, VP Global Sales.

    You will be responsible for all revenue generation in the following list of
    accounts:

-   DuPont (All divisions globally)

-   Rhone Poulenc (All divisions globally except HMR and Ariad-HMR)

-   Eli Lilly (All divisions globally)

-   Monsanto (All divisions globally)

-   Abbott (All divisions globally)

-   Schering Plough (All divisions globally)

-   SmithKline Beecham (All divisions globally, existing rep gets 10% on
          business closed in the next three months)

-   Sereno (All divisions globally)

-   Sanofi (All divisions globally)

-   Novartis Pharmaceutical divisions

-   Pfizer (50/50 split with Neil) [Timeframe (Through 12/31/99)]

-   Parke-Davis (50/50 split with Neil) [(Through 12/31/99)]

        Affiliates of the above named companies are not included in your
        territory. In case of any disputes, my decision shall be final and
        prevail.

        Your 1999 quota will be $1.5 million dollars software license revenue
        for the period April 19-December 31. First year maintenance is counted
        as software license revenue included for quota purposes. [This year and
        next 2 years.]

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                                      -2-

2.  Your base salary shall be $80,000 per annum payable in 24 semi-monthly
    installments. Your 1999 commission rate will be as follows:

    Commission for sales until December 31, 1999:

-     6.6% until achievement of $1,500,000 revenue

-     10% until achievement of $3,000,000 revenue. $15,000 bonus at $3,000,000.

-     10% until achievement of $4,500,000 revenue. $30,000 bonus at $4,500,000.

-     10% until achievement of $6,000,000 revenue. $45,000 bonus at $6,000,000.

-     13% commission rate after achievement of $6,000,00.

    Your Fiscal Year 2000 total compensation plan (base plus commission) will be
    $225,000 based on a quota of $2.5 Million if you achieve your 1999 quota.
    Your Fiscal Year 2001 total compensation (base plus commission) will be
    $250,000 based on a quota of $3 Million. If you achieve your 1999 quota,
    your over plan commissions in 2000 and 2001 will be based on your 1999 plan
    percentages.

3.  The Equity Incentive Compensation committee of the Board has approved an
    award of 20,000 incentive stock options for you under the company's Plan
    which will vest evenly over a 48 month period. If you achieve $3 Million
    software license revenue in 1999, 10,000 of your options will be fully
    vested and replaced with additional options which will vest over 48 months.
    If you achieve $4 million in software license revenue in 1999, 20,000 of
    your options will be accelerated and replaced.

4.  You will receive the standard company benefit plan which includes health and
    dental insurance, and a three week paid vacation. All approved and
    appropriately documented expenses will be reimbursed promptly.

5.  As a condition of employment, you will be required to sign the company's
    confidentiality and non-solicitation agreements.

6.  You understand that you are an at-will employee. You may be terminated with
    or without cause. Should you be terminated you will receive two weeks
    severance. [without cause, 4 weeks]

If the above correctly described our understanding, please sign this letter and
return to me (fax or email) I will provide you with the Confidentiality
Agreement and a hard cop of this letter for your signature when you arrive here
next week.

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                                   -3-

Sincerely,

/s/ Timothy D. Sullivan
Timothy D. Sullivan
Senior Vice President
Marketing and Sales

This letter accurately reflects my understanding of the terms of my employment
with InforMax.

/s/ Richard D. Melzer
Richard Melzer

Date:  4/16/99

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