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                                 EXHIBIT 10.5.1
 
                           ADVANCE ROYALTY AGREEMENT
 
    THIS ROYALTY ADVANCE AGREEMENT (the "Agreement") is made this 9th day of
January, 1997, by and between Boehringer Mannheim GmbH ("BM"), a German
corporation, having a principal place of business at Sandhofer Strasse 116,
D-6800 Mannheim 31, Federal Republic of Germany, and IGEN International
Incorporated ("IGEN"), a Delaware corporation, having a principal place of
business at 16020 Industrial Drive, Gaithersburg, Maryland 20877, with reference
to the following facts:
 
    A. IGEN and BM are parties to a License and Technology Development Agreement
dated as of September 23, 1992 (the "License Agreement"), pursuant to which,
among other things, IGEN granted to BM certain licenses to make, use and sell
certain instruments and assays based upon the ECL Technology, as such term is
defined in the License Agreement.

    B. IGEN and BM now desire to enter into an agreement whereby BM will 
advance to IGEN royalties that will become due under the License Agreement. 
THEREFORE, in consideration of the foregoing premises and the mutual 
covenants herein set forth, IGEN and BM do hereby agree as follows:
 
                                 1. DEFINITIONS 

    As used herein, capitalized terms shall have the respective meanings set 
forth below. All capitalized terms used herein and not defined in this 
Section 1 shall have the meaning given them in the License Agreement.

    1.1   "Advance Royalty Account" means an account on IGEN's books that
           reflects the amount, as it may increase as a result of interest
           accrual and decrease as a result of Royalties earned by IGEN, to be
           credited to BM pursuant to Section 2 hereof.

    1.2    "Collateral" means IGEN's rights under the License Agreement to
           receive Royalties from BM, all IGEN accounts receivable from BM with
           respect to Royalties earned under the License Agreement, the monies
           due and to become due under the License Agreement, and in all
           proceeds of such accounts.

    1.3    "Default" means the occurrence of any one or more of the following
           events (including the passage of time, if any, specified therefor):
           (i) IGEN shall become insolvent, fail to pay its debts generally as
           they become due, voluntarily seek, consent to, or acquiesce in the
           benefit or benefits of any IGEN Relief Law, or become a party to ( or
           be made the subject of) any proceeding provided for by any IGEN
           Relief Law, other than as a creditor or claimant, that could suspend
           or otherwise adversely affect the rights of BM hereunder (unless, in
           the event such proceeding is involuntary, the petition instituting
           same is dismissed within 60 days of the filing of same); (ii) the
           failure to have discharged within a period of 30 days after the
           commencement thereof any attachment, sequestration, or similar
           proceeding against any of the assets of IGEN; (iii) IGEN fails to pay
           any money judgment against it at least ten days prior to the date on
           which any of the assets of IGEN may be lawfully sold to satisfy such
           judgment; or (iv) the acceleration by the holder thereof of the
           maturity of any indebtedness owned by IGEN.

    1.4    "Debtor Relief Law" means the Bankruptcy Code of the United States of
           America and all other applicable liquidation, conservatorship,
           Bankruptcy, moratorium, rearrangement, receivership, insolvency,
           reorganization, suspension of payments, or similar IGEN relief laws
           from time to time in effect affecting the rights of creditors
           generally.

    1.5    "Interest Rate" means the sum of (i) [          ] as reported in the
           Wall Street Journal, Midwest Edition, on the morning of January 13,
           1997; plus (ii) [          ].

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    1.6    "Royalties" means the royalty payments due IGEN from BM pursuant to
           Section 6.2 and 6.3 of the License Agreement.

    1.7    "Sales Report" means the quarterly accounting of Net Sales of
           Products by BM and its Affiliate Sublicensees provided by IGEN by BM
           pursuant to Section 7.1 of the License Agreement.

    1.8    "Security Interest" means the security interest granted and the
           pledge and assignment made under Section 3.
 
                               2. ADVANCE ROYALTY
 
    2.1    ADVANCE ROYALTY.  BM hereby agrees to pay to IGEN, on or before
           January 13, 1997, the sum of Six Million United States Dollars
           ($6,000,000). Such sum shall be paid by wire transfer of immediately
           available funds to:
 
           Bank: [         ]
 
           Account Number: [          ]
 
           Account Name:
 
           ABA Number: [          ]
 
           Reference: "For further credit to IGEN, Inc."
 
IGEN agrees to immediately reflect such sum as a credit to BM in the Advance
Royalty Account.
 
    2.2    INTEREST.  The sum in the Advance Royalty Account shall accrue
           interest at the Interest Rate, compounded annually. Such interest
           shall be treated as a further credit to BM.
 
    2.3    CURRENT BALANCE OF ACCOUNT.  Within fifteen (15) days after receiving
           BM's quarterly Sales Report, IGEN shall advise BM in writing of the
           balance of the Advance Royalty Account as of the end of such quarter.
 
    2.4    PAYMENT OF ROYALTIES.  BM's payment to IGEN and the establishment of
           the Advance Royalty Account in accordance with Section 2.1 hereof
           constitute a pre-payment of Royalties which otherwise would have
           become due and payable to IGEN from BM pursuant to Section 6.2 and
           6.3 of the License Agreement. So long as there is a balance of
           greater than zero in the Advance Royalty Account, all such Royalties
           reflected in each Sales Report delivered by BM to IGEN shall
           automatically be deducted from and reduce the balance of the Advance
           Royalty Account as of the sixtieth day following the end of the
           quarter which was the subject of the Sales Report. In the event that
           the amount of Royalties due from BM to IGEN as reflected in a Sales
           Report exceeds the balance of the Advance Royalty Account, BM shall
           remit to IGEN with such Sales Report a payment reflecting the
           difference between the balance of the Advance Royalty Account as of
           the due date for such Sales Report and the amount of Royalties due as
           reflected in such Sales Report.
 
                              3. SECURITY INTEREST
 
    3.1    GRANT OF SECURITY INTEREST.  As security for IGEN's obligation to
           credit BM for Royalties due, IGEN here grants to BM a security
           interest in the Collateral.
 
    3.2    COVENANT OF IGEN.  So long as the balance of the Advance Royalty
           Account is greater than zero, IGEN agrees that:

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           (a)   it will not, without the prior written consent of BM, pledge or
                 grant any security interest in the Collateral to anyone except
                 BM, or permit any lien or encumbrance to attach to the
                 Collateral, or any levy to be made on the Collateral, or any
                 financing statement(except BM's statement) to be on file with
                 respect to the Collateral;
 
           (b)   it will not relocate IGEN's principal place of business, chief
                 executive office, or place where IGEN's books and records
                 related to accounts are kept, unless prior thereto IGEN
                 (i) gives BM 30 days prior written notice of such proposed
                 relocation (such notice to include, without limitation, the
                 name of the county or parish and state into which such
                 relocation is to be made) and (ii) (unless the relocation is to
                 a jurisdiction in which existing financing statements or other
                 required filings have previously been made to perfect the
                 Security Interest in such Collateral) executes and delivers all
                 such additional acts as BM in its sole discretion may request
                 in order to continue or maintain the existence and priority of
                 the Security Interest in such Collateral.
 
           (c)   it will, from time to time, promptly execute and deliver to BM
                 all such other assignments, certificates, supplemental
                 documents, and financing statements, and do all other acts or
                 things as BM may reasonably request in order to more fully
                 create, evidence, perfect, continue, and preserve the priority
                 of the Security Interest.
 
    3.3    REMEDIES.  Should a Default occur and be continuing, BM may, at its
           election, exercise any and all rights and remedies available to a BM
           under the Uniform Commercial Code, in addition to any and all other
           rights available to BM at law, in equity, or otherwise, including,
           without limitation, (a) reduce any claim to judgment; (b) exercise
           the rights of offset against the interest of IGEN in and all amounts
           due IGEN from BM to the extent of the full amount of the Advance
           Royalty Account; (c) foreclose the Security Interest and any other
           Liens BM may have or otherwise realize upon any and all of the rights
           BM may have in and to the Collateral, or any part thereof; or (d)
           applying by appropriate judicial proceedings for appointment of a
           receiver for all or part of the Collateral (and IGEN hereby consents
           to any such appointment).
 
                                4. MISCELLANEOUS
 
    4.1    TERM.  At such time as the balance of the Advance Royalty Account is
           reduced to zero, this agreement shall thereafter terminate upon
           receipt by BM of IGEN's written notice of such termination.
 
    4.2    ACTIONS NOT RELEASES.  The Security Interest and IGEN's obligations
           and BM's rights hereunder shall not be released, diminished,
           impaired, or adversely affected by the occurrence of any one or more
           of the following events: (i) the taking or accepting of any other
           security or assurance for any or all of IGEN's obligation under the
           License Agreement or hereunder; (ii) any release, surrender,
           exchange, subordination, or loss of any security or assurance at any
           time existing in connection with any or all of IGEN's obligations
           under the License Agreement or hereunder; (iii) the insolvency,
           bankruptcy, or lack of corporate or trust power of any party at any
           time liable for the performance of any or all of IGEN's obligations
           under the License Agreement or hereunder, whether now existing or
           hereafter occurring; (iv) any neglect, delay, omission, failure, or
           refusal of BM to take or prosecute any action in connection with any
           other agreement, document, guaranty, or instrument evidencing,
           securing, or assuring the performance of all or any of IGEN's
           obligations under the License Agreement or hereunder; (v) any failure
           of BM to notify IGEN of any renewal, extension, or assignment of
           IGEN's obligations under the License Agreement or Hereunder or any
           part thereof, or the release of any security, or of any other action
           taken or refrained from being taken by BM against IGEN or any new
           agreement between BM and IGEN; (vi) the illegality, invalidity, or
           unenforceability of all or any part of IGEN's obligations under the
           License Agreement or hereunder against any party obligated with
           respect thereto by reason of the fact that the act of creating IGEN's
           obligations under the License Agreement or hereunder, or any

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           part thereof, is ultra vires, or the officers creating same acted in
           excess of their authority, or for any other reason; or (vii) if any
           payment by any party obligated with respect thereto is held to
           constitute a preference under applicable laws or for any other
           reason BM is required to refund such payment or pay the amount
           thereof to someone else. 

    4.3    Captions: Arrangements. The headings, captions, and arrangements used
           herein are, unless specified otherwise, for convenience only and
           shall not be deemed to limit, amplify, or modify the terms hereof nor
           affect the meaning thereof. Whenever herein the singular number is
           used, the same shall include the plural where appropriate, and vice
           versa; and words of any gender herein shall include each other gender
           where appropriate. The words "herein," "hereof," and "hereunder," and
           other words of similar import refer to this agreement as a whole and
           not to any particular part or subdivision hereof.
 
    4.4    NOTICES.  Any notice or other communication required or permitted to
           be given to either party hereto shall be in writing and shall be
           deemed to have been properly given to be effective on the date of
           delivery if delivered in person or by facsimile or five days after
           mailing by registered or certified mail, postage paid, to the other
           party at the address specified for notice to such party in the
           License Agreement.
 
    4.5    GOVERNING LAW.  This agreement is being executed and delivered, and
           is intended to be performed, in the state of Maryland, and the laws
           of such state and of the United States of America shall govern the
           rights and duties of the parties hereto and the validity,
           construction, enforcement, and interpretation hereof.
 
    4.6    INVALID PROVISIONS.  If any provision hereof is held to be illegal,
           invalid, or unenforceable under present or future laws effective
           during the term hereof, such provision shall be fully severable; this
           agreement shall be constructed and enforced as if such illegal,
           invalid, or unenforceable provision had never comprised a part
           hereof; and the remaining provision hereof shall remain in full force
           and effect and shall not be affected by the illegal, invalid, or
           unenforceable provision or by its severance here from. Furthermore,
           in lieu of such illegal, invalid, or unenforceable provision there
           shall be added automatically as a part hereof a provision as similar
           in terms to such illegal, invalid, or unenforceable provision as may
           be possible and be legal, valid, and enforceable.
 
    4.7    ENTIRETY AND AMENDMENTS.  This instrument and the License Agreement
           embody the entire agreement between the parties, supersede all
           prior agreements and understandings, if any, relating to the subject
           matter hereof, and may be amended only by an instrument in writing
           executed jointly by an authorized officer of each party hereto and
           supplemented only by documents delivered or to be delivered in
           accordance with the express terms hereof.
 
    4.8    MULTIPLE COUNTERPARTS.  This agreement may be executed in a number
           of identical counterparts, each of which shall be deemed an original
           for all purposes and all of which constitute, collectively, one
           agreement; but in making proof of this agreement, it shall not be
           necessary to produce or account for more than one such counterpart.
 
    4.9    PARTIES BOUND; ASSIGNMENT.  This agreement shall be binding on IGEN
           and IGEN's successors, and assigns and shall inure to the benefit of
           BM and BM's successors and assigns. Neither party may, without the
           prior written consent of the other, assign any of its rights, duties
           or obligations hereunder, and any such attempted assignment shall be
           void. 

                          (next page is signature page)

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IN WITNESS WHERE OF, the parties have executed this Agreement to be effective as
of the date first written above.
 
BOEHRINGER MANNHEIM GMBH                  IGEN INTERNATIONAL INCORPORATED
 
ppa.
/ /

/ /
/s/ Walter Funk                           /s/ George Migausky
-------------------------------           -------------------------------
Title:  Senior Vice President             Title:  Chief Financial Officer
        Accounting and Finance

ppa.

/s/ Klaus Gilow
-------------------------------
Title:  Senior Vice President Legal

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