<PAGE>

                                                                    EXHIBIT 10.4

[PERKINELMER LOGO]                              -  Richard F. Walsh
                                                   Senior Vice President
                                                   Human Resources

                                                -  PerkinElmer, inc
                                                   45 William Street
                                                   wellesley, MA 02481
                                                   T:781-431-4122
                                                   F:781-431-4183
                                                   richard.walsh@perkinelmer.com

VIA UPS

December 13, 2002

John J. Engel
12 Longmeadow Drive
Westwood, MA 02090

Dear John:

As we have agreed, your employment with PerkinElmer, Inc. (the "Company") ended
on November 15, 2002. To assist you during this transition period and in
exchange for your agreement to the terms and conditions set forth herein, the
Company will pay you the severance benefits described in the "Description of
Severance Benefits" attached as Attachment A if you timely sign and return this
letter by December 31, 2002. By signing and returning this letter you will be
agreeing to the terms and conditions set forth in the numbered paragraphs below,
including the release of claims set forth in paragraph 3 and restrictive
covenants set forth in paragraph 6. You are advised to consult with your
attorney before signing this letter and you have been given at least twenty-one
(21) days to do so. If you sign this letter, you may change your mind and revoke
your agreement during the seven (7) day period after you have signed it by
notifying Richard F. Walsh in writing. If you do not so revoke, this letter will
become a binding agreement between you and the Company upon the expiration of
the seven (7) day revocation period.

If you choose not to sign and return this letter agreement by December 31, 2002,
you shall not be eligible to receive any severance benefits from the Company,
and except as expressly provided in this paragraph, all of your other benefits,
including life insurance and long-term disability, will cease upon the
Termination Date. You will, however, receive payment for any unused vacation
time accrued through your termination date. Also, even if you decide not to sign
this letter agreement, you may elect to continue receiving group medical
insurance pursuant to the federal "COBRA" law, 29 U.S.C. Section 1161 et seq.
All premium costs shall be paid by you on a monthly basis for as long as, and to
the extent that, you remain eligible for COBRA continuation. You should consult
the COBRA materials to be provided by the Company for details regarding these
benefits.

If, after reviewing this letter agreement with your attorney, you find the terms
and conditions are satisfactory to you, you should sign and return this letter
to Richard Walsh by December 31, 2002.

The following numbered paragraphs set forth the terms and conditions which will
apply if you timely sign and return this letter agreement and do not revoke it
within the seven (7) day revocation period:

1.       TERMINATION DATE AND TRANSITIONAL DUTIES - Your effective date of
         termination from the Company was November 15, 2002 (the "Termination
         Date"). You agree that you will provide transitional assistance through
         December 31, 2002 to the Company, as such assistance is requested by
         Greg Summe.
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John J. Engel
December 13, 2002
Page 2

2.       DESCRIPTION OF SEVERANCE BENEFITS - The severance benefits paid to you
         if you timely sign and return this letter and do not revoke it within
         the seven (7) day revocation period are described in the "Description
         of Severance Benefits" attached as Attachment A.

3.       RELEASE - In consideration of the severance benefits, to which you
         acknowledge you would not otherwise be entitled, you hereby fully,
         forever, irrevocably and unconditionally release, remise and discharge
         the Company, its current or former officers, directors, stockholders,
         corporate affiliates, parents, subsidiaries, attorneys, agents and
         employees (the "Released Parties") from any and all claims, charges,
         complaints, demands, actions, causes of action, suits, rights, debts,
         sums of money, costs, accounts, reckonings, covenants, contracts,
         agreements, promises, doings, omissions, damages, executions,
         obligations, liabilities, and expenses (including attorneys' fees and
         costs), of every kind and nature which you ever had or now have against
         any of the Released Parties, including, but not limited to, all
         employment discrimination claims under Title VII of the Civil Rights
         Act of 1964, 42 U.S.C. Section 2000e et seq., the Age Discrimination in
         Employment Act, 29 U.S.C., Section 621 et seq., the Americans With
         Disabilities Act, 42 U.S.C., Section 12101 et seq., the Family and
         Medical Leave Act, 29 U.S.C. Section 2601 et seq., and the
         Rehabilitation Act of 1973, 29 U.S.C. Section 701 et seq., all as
         amended; all claims arising out of the Employment Retirement Income
         Security Act of 1974, 29 U.S.C. Section 1001 et seq., and the Worker
         Adjustment and Retraining Notification Act, 29 U.S.C. Section 2101 et
         seq., all as amended; the Massachusetts Fair Employment Practices Act.,
         M.G.L. c.l51B, Section 1 et seq., the Massachusetts Civil Rights Act,
         M.G.L. c.12 Sections 1lH and 11l, the Massachusetts Equal Rights Act,
         M.G.L. c.93, Section 102 and M.G.L. c.214, Section 1C, the
         Massachusetts Labor and Industries Act, M.G.L. c.149, Section 1 et
         seq., and the Massachusetts Privacy Act, M.G.L. c. 214, Section 1B, all
         as amended; all common law claims including, but not limited to,
         actions in tort, defamation and breach of contract; all claims to any
         non-vested ownership interest in the Company, contractual or otherwise,
         including but not limited to claims to stock or stock options; any
         claims under your December 1, 1999 Employment Agreement; and any claim
         or damage arising out of your employment with or separation from the
         Company (including a claim for retaliation) under any common law theory
         or any federal, state or local statute or ordinance not expressly
         referenced above; provided, however, that nothing in this Agreement
         prevents you from filing, cooperating with, or participating in any
         proceeding before the EEOC or a state Fair Employment Practices Agency
         (except that you acknowledge that you may not be able to recover any
         monetary benefits in connection with any such claim, charge or
         proceeding); and provided further that you are not waiving or releasing
         any right you have for indemnification in accordance with the terms of
         any Company by-law or article of incorporation, under the Company's
         Directors and Officers insurance policy, or pursuant to any applicable
         statute in any matter in connection with your employment, including,
         where applicable, any rights you have for reimbursement of attorney's
         fees or costs.

4.       NON-DISCLOSURE - You acknowledge your obligation to keep confidential
         all non-public information concerning the Company which you acquired
         during the course of employment with the Company. As stated more fully
         in the Employee Patent and Proprietary Information Utilization
         Agreement signed by you in favor of the Company (which remains in full
         force and effect), you will not disclose any such information to, or
         use such information for, the benefit of any third party, including
         competitors of the Company.

5.       NON-DISPARAGEMENT - You understand and agree that as a condition for
         payment to you of the severance benefits herein described, you shall
         not make any false, disparaging or derogatory statements to any media
         outlet, industry group, financial institution or current or former
         employee, consultant, client or customer of the Company regarding the
         Company or any of its directors, officers, employees, agents or
         representatives or about the Company's business affairs and
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John J. Engel
December 13, 2002
Page 3

         financial condition. The Company shall direct those directors, officers
         and employees who are privy to the terms of this Agreement, i.e., Greg
         Summe, Terry Carlson, Robert Friel, and Rich Walsh, not to make any
         false, disparaging or derogatory statements regarding you, provided,
         that nothing in this sentence shall prevent the Company from acting as
         it deems appropriate in connection with any claims, inquiries, actions,
         or investigatory proceedings which have been brought, or which may be
         brought in the future against or on behalf of the Company or any of its
         current or former officers, whether before a state or federal court,
         any state or federal government agency, or any self-regulating
         organization, including, but not limited to, making any public
         statement in response to any such claims, inquiries, actions, or
         investigatory proceedings.

6.       NON-SOLICITATION AND NON-COMPETITION - You understand and agree that as
         a condition for payment to you of the severance benefits herein
         described, you shall not, for a period of two (2) years from the
         Termination Date, directly or indirectly: (i) as an individual
         proprietor, partner, stockholder, officer, employee, director, joint
         venture, investor, lender, or in any other capacity whatsoever (other
         than as the holder of not more than one percent (1%) of the total
         outstanding stock of a publicly held company), engage directly or
         indirectly in any business or entity identified in Attachment B hereto,
         except as approved in advance by the Board after full and adequate
         disclosure; or (ii) recruit, solicit or induce, or attempt to induce,
         any employee or employees of the Company to terminate their employment
         with, to otherwise cease their relationship with, the Company; or (iii)
         solicit, divert or take away, or attempt to divert or to take away, the
         business or patronage of any of the clients, customers or accounts, of
         the Company that were contacted, solicited or served by you while you
         were employed by the Company. You acknowledge that the restrictions
         contained in this paragraph are necessary for the protection of the
         business and goodwill of the Company, consider the restrictions to be
         reasonable for such purpose. You agree that any breach of this
         paragraph 6 is likely to cause the Company irreparable damage, and
         therefore, in the event of such a breach, in addition to such other
         remedies which may be available, the Company shall have the right to
         seek specific performance and injunctive relief without posting a
         bond.

7.       COMPANY PROPERTY - You confirm that, to the extent that you have any
         Company-owned property listed or described below in your possession or
         control, you will return to the Company, on or before December 31,
         2002, all Company-owned property, including, but not limited to keys,
         files, records (and copies thereof), equipment (including, but not
         limited to, computer hardware, software and printers, wireless handheld
         devices, cellular phones, pagers, etc.), Company identification,
         Company vehicles and any other Company-owned property in your
         possession or control. You acknowledge and confirm that this obligation
         to return Company-owned property extends to all documents, memoranda,
         drafts, notes, and computer files and software, including such
         materials that have been produced by you in connection with your
         employment with the Company, which are in your possession or control.
         You further confirm that to the best of your knowledge, you have not
         improperly destroyed or modified any electronic Company documents,
         including but not limited to those which you developed or help develop
         during your employment. To the extent that you have electronic Company
         documents in your possession or control through a personal computer or
         other device, you will provide the Company with a copy of such
         documents, and immediately delete of all such files from your personal
         computer or other device. Finally, you confirm that by December 31,
         2002, you will have cancelled all accounts for your benefit, if any, in
         the Company's name, including but not limited to, credit cards,
         telephone charge cards, cellular phone and/or pager accounts and
         computer accounts.

8.       COOPERATION IN LITIGATION AND OTHER PROCEEDINGS - Except as provided
         herein, you agree to cooperate fully with the Company in the defense or
         prosecution of any claims, inquiries, actions
<PAGE>
John J. Engel
December 13, 2002
Page 4

         or investigatory proceedings relating to matters of which you could
         have knowledge due to your employment with the Company, which have been
         brought, or which may be brought in the future against or on behalf of
         the Company or any of its current or former officers, whether before a
         state or federal court, any state or federal government agency, or any
         self-regulating organization. Your full cooperation in connection with
         such claims, inquiries, actions or proceedings shall include, but not
         be limted to, being available to meet with counsel to prepare any
         claims or defenses, to prepare for trial or discovery or an
         administrative hearing and to act as a witness when requested by the
         Company at mutually agreed upon reasonable times. In situations in
         which you believe that cooperation would lead to a detriment to your
         own defense in the same or related pending or threatened proceeding,
         the Company agrees to permit you to limit your cooperation as it
         determines reasonable.. The Company will provide you with reasonable
         travel and related expenses in connection with your cooperation, and
         may, in its discretion, provide you with the option of representation
         by Company-provided counsel

9.       AMENDMENT - This letter agreement shall be binding upon the parties and
         may not be modified in any manner, except by an instrument in writing
         of concurrent or subsequent date signed by duly authorized
         representatives of the parties hereto. This letter agreement is binding
         upon and shall inure to the benefit of the parties and their respective
         agents, assigns, heirs, executors, successors and administrators.

10.      WAIVER OF RIGHTS - No delay or omission by the Company in exercising
         any right under this letter agreement shall operate as a waiver of that
         or any other right. A waiver or consent given by the Company on anyone
         occasion shall be effective only in that instance and shall not be
         construed as a bar or waiver of any right on any other occasion.

11.      VALIDITY - If any restriction set forth in paragraph 6 above is found
         by any court of competent jurisdiction to be unenforceable because it
         extends for too long a period of time or over too great a range of
         activities or in too broad a geographic area, it shall be interpreted
         to extend only over the maximum period of time, range of activities or
         geographic area as to which it may be enforceable. Should any provision
         of this letter agreement be declared or be determined by any court of
         competent jurisdiction to be illegal or invalid, the validity of the
         remaining parts, terms or provisions shall not be affected thereby and
         said illegal and invalid part, term or provision shall be deemed not to
         be a part of this letter agreement.

12.      CONFIDENTIALITY - You understand and agree that as a condition for
         payment to you of the severance benefits herein described, the terms
         and conditions of this letter agreement, and the contents of any
         negotiations and discussions resulting in this letter agreement, shall
         be maintained as confidential by you and your agents and
         representatives and shall not be disclosed to any third party except to
         the extent required by an order of a court or agency, by federal or
         state law, or as otherwise agreed to in writing by the Company,
         provided that you may discuss this letter agreement with your immediate
         family, financial advisors, and attorneys. Likewise, the Company agrees
         to instruct those directors, officers and employees who are privy to
         the terms and conditions of this letter agreement, and the contents of
         any negotiations and discussions resulting in this letter agreement, to
         maintain such information as confidential and not to disclose such
         information to any third party outside of the Company, except to the
         extent required by an order of a court or agency, by federal or state
         law, including with out limitation, applicable securities laws, by the
         rules of the New York Stock Exchange, or as otherwise agreed to in
         writing by you.
<PAGE>
John J. Engel
December 13, 2002
Page 5

13.      NATURE OF AGREEMENT - You and the Company understand and agree that
         this letter agreement is a severance agreement and does not constitute
         an admission of liability or wrongdoing on the part of you, the
         Company, or any other person.

14.      ACKNOWLEDGMENTS - You acknowledge that you have been given at least
         twenty-one (21) days to consider this letter agreement, including
         Attachments A and B, and that the Company advised you to consult with
         an attorney of your own choosing prior to signing this letter
         agreement. You understand that you may revoke this letter agreement for
         a period of seven (7) days after you sign this letter agreement, and
         the letter agreement shall not be effective or enforceable until the
         expiration of this seven (7) day revocation period.

15.      VOLUNTARY ASSENT - You affirm that no other promises or agreements of
         any kind have been made to or with you by any person or entity
         whatsoever to cause you to sign this letter agreement, and that you
         fully understand the meaning and intent of this agreement. You state
         and represent that you have had an opportunity to fully discuss and
         review the terms of this letter agreement, including Attachments A and
         B, with an attorney. You further state and represent that you have
         carefully read this letter agreement, including Attachments A and B,
         understand the contents therein, freely and voluntarily assent to all
         of the terms and conditions thereof, and sign your name of your own
         free act.

16.      APPLICABLE LAW - This letter agreement shall be interpreted and
         construed by the laws of the Commonwealth of Massachusetts, without
         regard to conflict of laws provisions. You hereby irrevocably submit to
         and acknowledge and recognize the jurisdiction of the state and federal
         courts of Massachusetts (which courts, together with all applicable
         appellate courts, for purposes of this letter agreement, are the only
         courts of competent jurisdiction) over any suit, action or other
         proceeding arising out of, under or in connection with this letter
         agreement or the subject matter hereof.

17.      ENTIRE AGREEMENT - This letter agreement, including Attachments A and
         B, contains and constitutes the entire understanding and agreement
         between the parties hereto with respect to your severance benefits and
         the settlement of claims against the Company and cancels all previous
         oral and written negotiations, agreements, commitments, and writings in
         connection therewith. Nothing in this paragraph, however, shall modify,
         cancel or supercede your obligations set forth in paragraph 4. Further,
         the terms of the 1999 Stock Option Agreement and the 2000 Restricted
         Stock Agreement between you and the Company, which are governed by the
         underlying plans, and the underlying plans, shall remain in full force
         and effect pursuant to their terms. The terms of your purchase of stock
         pursuant to, and governed by, the Employee Stock Purchase Plan, as well
         as the Employee Stock Purchase Plan, the terms of the deferral of any
         stock or other compensation pursuant to, and governed by, the Deferred
         Compensation Plan, and the Deferred Compensation Plan, and the terms of
         your contributions and Company matching to your 401(k) account pursuant
         to, and governed by the 401(k) Plan and the 401(k) Plan document shall
         remain in full force and effect pursuant to the terms of such plans.

If you have any questions about the matters covered in this letter, please
contact me.
<PAGE>
John J. Engel
December 13, 2002
Page 6

Very truly yours
PerkinElmer, inc.

By: /s/ Richard F. walsh
    -------------------------------------
    Richard F. Walsh
    Senior Vice President, Human Resources

I hereby agree to the terms and conditions set forth above and in Attachments A
and B, and set my hand and seal to my agreement as of the date set forth below.
I have been given at least twenty-one (21) days to consider this letter
agreement (including Attachments A and B) and I have chosen to execute this on
the date below. I intend that this letter agreement will become a binding
agreement between the Company and me if I do not revoke my acceptance in seven
(7) days.

/s/ John J. Engel                        December 23, 2002
------------------------------           -----------------
John J. Engel                                   Date

To be returned to Richard F. Walsh by December 31, 2002.
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John J. Engel
December 13, 2002
Page 7

                                  ATTACHMENT A

                        DESCRIPTION OF SEVERANCE BENEFITS

If you timely sign and return this letter agreement and it becomes binding, the
Company will provide you with the following benefits:

SALARY CONTINUATION
The Company will provide you with continuation of your base salary through
December 31, 2003 (the "Salary Continuation Period"), less all applicable state
and federal taxes, as severance pay. The Company also will pay you an amount
through December 31, 2003, equal to the amount you would have received for
mortgage assistance, including gross-up for taxes due on the mortgage
assistance, through that time period had you remained employed by the Company.
These payments will be paid in accordance with the Company's normal payroll
practices, and will commence no earlier than the eighth (8th) day after this
letter agreement becomes binding.

BONUS PAYMENTS
The Company will pay you the amount equal to your target bonus for the
performance period beginning July 1, 2002 and ending December 31, 2002 under the
Performance Incentive Plan (PIP) ($140,000.00), less all applicable state and
federal taxes. In addition, the Company will provide you with an additional
payment of ($140,000.00), less all applicable state and federal taxes. These
payments will be paid prorata throughout the Salary Continuation Period in
accordance with the Company's normal payroll procedures, and will commence no
earlier than the eighth (8th) day after this letter agreement becomes binding.

LOAN REPAYMENT
Before December 31, 2003, you will repay the Company the principal amount of
your interest free loan ($250,000). As required by US tax laws, the Company will
calculate imputed interest income while the loan is outstanding and will include
an amount in your W-2 form for the imputed interest and gross-up for taxes due
on the imputed interest.

BENEFITS CONTINUATION
You will also be eligible to continue to participate in the same medical,
dental, life, and accidental death and disability coverage as you had while you
were employed with PerkinElmer as well as to continue to receive the automobile
allowance (of $17,500 per year, minus applicable taxes and withholdings) and
financial counseling allowance (of $12,000 per year, minus applicable taxes and
withholdings) you received while you were employed by the Company during the
Salary Continuation Period, to the same extent and upon the same terms as were
in effect immediately prior to the Termination Date (except that, for federal
income tax purposes, you will be treated as a former employee). Thereafter, you
may elect to continue receiving group medical insurance pursuant to the federal
"COBRA" law, 29 U.S.C. Section 1161 et seq. If you make that election, all
premium costs shall be paid by you on a monthly basis for as long as, and to the
extent that, you remain eligible for COBRA continuation. You should consult the
COBRA materials to be provided by the Company for details regarding these
benefits.

401(k) EXCESS PROGRAM FOR 2002
The Company will provide you with a payment of $13,200 ($400,000 X .06 X .55)
under the 401(k) Excess Program for 2002 based on a base salary of $400,000,
less all applicable state and federal taxes.
<PAGE>
John J. Engel
December 13, 2002
Page 8

You are not eligible to receive a Company match in the 401(k) plan for 2002
because you will not be an active employee on 12/31/02.

OUTPLACEMENT
Outplacement services for will be arranged for you. Further information on
outplacement services will be provided under separate cover.
<PAGE>
John J. Engel
December 13, 2002
Page 9

                                  ATTACHMENT B

                   LIST OF COMPANIES COVERED BY PARAGRAPH 6(i)

The list of companies covered by paragraph 6(i) is shown below and includes
these entities even though names may change through merger or other corporate
transactions.

         1.  Agilent, Inc.

         2.  ThermoElectron Corporation or any of its direct or indirect
             subsidiaries

         3.  Varian, Inc.

         4.  Waters Corporation

         5.  Bio-Rad Laboratories

         6.  Applera Corp or any of its direct or indirect subsidiaries

         7.  Amersham Pharmacia Biotech Inc.

         8.  Affymetrix, Inc.

         9.  Invitrogen Corp

         10. Molecular Devices Corp

         11. Mettler Toledo International, Inc.

         12. Dpix

         13. Hamamatsu Photonics, K.K.

         14. Zymark Corporation

         15. Beckman Coulter