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Exhibit 10.328

CONFIDENTIAL   REDACTED VERSION

[***] CERTAIN INFORMATION IN THIS EXHIBIT HAS BEEN OMITTED AND FILED SEPARATELY
WITH THE COMMISSION. CONFIDENTIAL TREATMENT HAS BEEN REQUESTED WITH RESPECT TO
THE OMITTED PORTIONS.

***CONFIDENTIAL TREATMENT REQUESTED***

FUTURE BLOOD SCREENING ASSAY—

WEST NILE VIRUS ADDENDUM

AMENDING

AGREEMENT ENTERED INTO AS OF JUNE 11, 1998

BY AND BETWEEN

GEN-PROBE INCORPORATED, A DELAWARE CORPORATION

AND

CHIRON CORPORATION

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TABLE OF CONTENTS

 
  Page

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1.    Definitions   2     1.1    Agreement   2     1.2    Alternative NAT
Clinical Diagnostic Product   2     1.3    Binder   2     1.4    Budget   2    
1.5    Completion Date   2     1.6    FTE Labor Rate   2     1.7    Interim
Events   2     1.8    Material Modification   2     1.9    NIH Monies   2    
1.10    Non-material Modification   2     1.11    Product Requirements Document
  3     1.12    Project Management   3     1.13    Resource Plan   3    
1.14    Software Requirements Specifications   3     1.15    Technical Plan   3
    1.16    Timeline   3     1.17    WNV Assay Product   3     1.18    WNV
Development Costs   3     1.19    WNV Development Program   3     1.20    WNV
Clinical Diagnostic Product   3 2.    WNV Development Program   3    
2.1    Objective   3     2.2    General Conduct of Development   4     2.3    No
Guarantee   4     2.4    Project Management   4         2.4.1.    Principles of
Project Management   4         2.4.2.    Project Manager   5        
2.4.3.    Project Manager's Responsibilities   5         2.4.4.    Project
Leaders   6         2.4.5.    Reports   6         2.4.6.    Meetings of the
Supervisory Board   6     2.5    Development Responsibilities   6        
2.5.1.    Principal Responsibility; General Statement   6        
2.5.2.    Shared Responsibility   7         2.5.3.    Principal and Shared
Responsibility; Specific Allocation   7         2.5.4.    Regulatory/Licensure  
7         2.5.5.    Project Leader Disagreements   7      

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3.    Modifications   8     3.1    WNV Development Program Definition   8    
3.2    Modifications   8         3.2.1.    Request for Modifications   8        
3.2.2.    Non-Material Modifications   8     3.3    Material Modifications   9  
      3.3.1.    Request for Material Modifications   9         3.3.2.    Initial
Analysis of Impact of Proposed Material Modification   9        
3.3.3.    Preparation of Modified WNV Development Program   9        
3.3.4.    Acceptance of Modified WNV Development Program   9        
3.3.5.    Effective Date of Modified WNV Development Program   10    
3.4    Notice of Significant Changes   10 4.    Changes to WNV Assay Product
after Completion Date   10     4.1    Process   10     4.2    Additional Work
under Addendum   11 5.    WNV Development Costs   11     5.1    [***] WNV
Development Costs   11         5.1.1.    [***]   11         5.1.2.    Prior to
Material Modification   11         5.1.3.    After Material Modification   12  
  5.2    Definition and Calculation of WNV Development Costs   12        
5.2.1.    WNV Development Costs; FTE Labor Rate   12        
5.2.2.    Comparison with Resource Plan   14         5.2.3.    Methodology   14
    5.3    Payment of WNV Development Costs   14         5.3.1.    Accrued WNV
Development Costs   14         5.3.2.    [***] Budgeted Payments   14        
5.3.3.    [***] True-Up Payments   14         5.3.4.    Invoices   15    
5.4    Additional Provisions regarding Shared Revenues   15        
5.4.1.    [***]   15         5.4.2.    [***]   15     5.5    Dispute   15    
5.6    Right to Audit and Verify   15 6.    Manufacturing and Commercialization
  15     6.1    Definitions Relevant to Manufacturing and Commercialization
Obligation   15         6.1.1.    Applicable Purchase Price   15        
6.1.2.    Transfer Price   16         6.1.3.    Manufacturing Cost   16        
6.1.4.    Rare Reagents   16     6.2    Right to Audit and Verify   16    
6.3    Non-Commercial Products   16     6.4    Commercialization Budget   17
7.    License Grants   17      

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8.    Addendum Effective Date; Term; Termination   18         Term of West Nile
Virus Addendum         8.1    Termination for Breach   18        
8.1.1.    Default   19         8.1.2.    Right to Cure Event of Default   19    
    8.1.3.    Effect of Termination for Breach   19     8.2    Termination by
Both Parties   19         8.2.1.    Vote to Terminate   19        
8.2.2.    Effect of Notice Period on Termination by Both Parties   19        
8.2.3.    Effect of Termination by Both Parties   20     8.3    Termination by
Either Party; Unilateral Withdrawal from WNV Development Program   20    
8.4    Continuance of WNV Development Program following Unilateral Withdrawal or
Termination   20         8.4.1.    Election   20         8.4.2.    Funding and
Conduct of Development   20         8.4.3.    Reimbursement of Development Costs
  21         8.4.4.    Control of the Program upon Unilateral Funding   21      
  8.4.5.    Rights under Agreement   21 9.    Escalation   22    
9.1    Escalation Process   22     9.2    Remedies in Event of Default   22    
9.3    Survival   22 10.    No Other Amendment   22 11.    Counterparts   23

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Future Blood Screening Assay—

WEST NILE VIRUS ADDENDUM

        This Future Blood Screening Assay—West Nile Virus Addendum (the "West
Nile Virus Addendum") is entered into, effective as of June 1, 2003 (the
"Addendum Effective Date") pursuant to and amending that certain Agreement
entered into as of June 11, 1998 (the "Agreement") by and between Gen-Probe
Incorporated, a Delaware corporation ("Gen-Probe") with a principal place of
business at 10210 Genetic Center Drive, San Diego CA 92121, and Chiron
Corporation, a Delaware corporation ("Chiron;" collectively with Gen-Probe, the
"parties") with a place of business at 4560 Horton Street, Emeryville, CA 94608.

Recitals

        A.    The parties entered into the Agreement as of June 11, 1998. The
Agreement was amended by the following: (i) June 11, 1998 Supplemental letter
agreement, (ii) June 26, 1998 Addendum to Collaboration Agreement,
(iii) June 30, 1998 Supplemental letter agreement, (iv) June 30, 1998 Consent,
(v) December 7, 1999 Amendment to Collaboration Agreement, (vi) February 1, 2000
Amendment No. 2 to Collaboration Agreement, (vii) June 7, 2001 Supplemental
agreement no. 1 (Customer training and Support), (viii) October 30, 2001
Confidentiality and Joint Interest Agreement, and (ix) April 1, 2002 Amendment
No. 3 (warehousing and shipping). In addition, the parties entered into certain
settlements, described in Recital E below.

        B.    In the Agreement, the parties agreed to discuss, during the term
thereof, the selection and establishment of one or more Development Programs for
one or more Future Blood Screening Assays to be conducted by the Blood Screening
Instruments.

        C.    The parties have discussed a proposed development of an assay for
the detection of West Nile Virus (WNV), on a semi-automated instrument system,
which assay would fall within the definition of a "Future Blood Screening Assay"
set forth in Section 1.30 of the Agreement and does not include HCV as a
constituent element.

        D.    Gen-Probe applied for and received a contract with the National
Institutes of Health, Contract No. NO1-HB-07148, effective January 1, 2000,
which contract as amended provides for, among other things, the partial funding
of costs associated with the development of the WNV Assay Product.

        E.    The parties submitted a number of disputes under the Agreement to
arbitration pursuant to Section 13 of the Agreement, and in resolution of those
disputes, executed a Definitive Written Settlement Agreement, dated December 5,
2001, and a Short Form Agreement, dated November 16, 2001. All provisions of
these settlement agreements which address the subject matter addressed in this
Addendum are expressly superceded by this West Nile Virus Addendum, except as
expressly described herein.

        F.     By this West Nile Virus Addendum, the parties desire to include
the West Nile Virus Assay to be conducted by one or more of the Blood Screening
Instruments within the scope of the provisions of the Agreement as clarified and
amended by the terms and conditions more particularly described in this West
Nile Virus Addendum.

        G.    The purpose of WNV development program is to meet an urgent need
in the United States, as articulated by FDA and industry, to provide an IND WNV
screening assay by July 1, 2003. The parties intend that, if a fully licensed
product becomes required and commercially appropriate, the terms applicable to
the development and distribution of that product will require a modification of
this Agreement.

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Agreement

        NOW, THEREFORE, for and in consideration of the mutual covenants and
agreements set forth in this West Nile Virus Addendum, the parties agree as
follows:

        1.    Definitions.    All capitalized terms used but not defined in this
West Nile Virus Addendum shall have the meanings set forth in the Agreement.

        1.1   Agreement shall have the meaning set forth in the first paragraph
of this West Nile Virus Addendum.

        1.2   Alternative NAT Clinical Diagnostic Product means the alternative
NAT product (reflected in the WNV Development Program shared responsibility
described in Section 2.5.3 below) developed by Chiron and sold in the Clinical
Diagnostic Field.

        1.3   Binder means that certain three-ring binder, with one or more
volumes, entitled "WNV Development Program for the WNV Assay Product
(Gen-Probe/Chiron WNV Development Addendum, dated as of            ) Binder," in
which certain documents, materials or other items incorporated into this West
Nile Virus Addendum by reference are kept. The original Binder and an additional
volume of the Binder, labeled "Amendments to WNV Development Program" and
reflecting any changes, modifications or amendments to the Binder, are
maintained by and located at the premises of Gen-Probe. A copy of the original
Binder, and a copy of the additional volume of the Binder, each signed by both
parties, shall be maintained by and located at the premises of Chiron.

        1.4   Budget means the written, approved budget of WNV Development Costs
for the WNV Development Program, including the estimated cost of the WNV
Development Program on a monthly basis through the end of the WNV Development
Program. The approved Budget is described in the Binder under the heading
"Budget", and may be amended from time to time under the provisions of Section 3
below.

        1.5   Completion Date means the earlier of (i) [***], or (ii) [***].

        1.6   FTE Labor Rate is defined in Section 5.2.1.

        1.7   Interim Events means such events of material significance to the
WNV Development Program as are mutually agreed to by both parties and set forth
with specificity and identified as an "Interim Event" on the Timeline included
within the Technical Plan, as such Interim Events may be modified, pursuant to
the change procedures set forth in Section 3 of this West Nile Virus Addendum.

        1.8   Material Modification means a change or amendment to the WNV
Development Program that materially affects the requirements set forth in the
then-current Product Requirements Document, Software Requirement Specifications,
Technical Plan, Resource Plan or Budget, or that materially modifies an Interim
Event set forth in the Timeline included within the Technical Plan.

        1.9   NIH Monies means all monies actually paid to Gen-Probe by the NIH
specifically to defray WNV Development Costs under (i) the NIH contract
referenced in Recital C above (ii) any extensions or amendments to the NIH
contract referenced in Recital C, and (iii) any other contract or grant under
which Gen-Probe seeks reimbursement for WNV Development Costs. NIH Monies shall
not include any monies paid to Gen-Probe by the NIH for any other purpose, even
if paid pursuant to contracts which also provide for payment of WNV Development
Costs so long as Gen-Probe can reasonably demonstrate that monies paid do not
relate to the WNV Development Program.

        1.10   Non-material Modification means a change or amendment to the WNV
Development Program other than a Material Modification. Written agreement among
members of Project

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Management that a modification is a "Non-material Modification" hereunder as
described in Section 3.2 below shall be conclusive.

        1.11   Product Requirements Document (or "PRD") means the specifications
for the WNV Assay Product, and includes as a component thereof the Software
Requirements Specifications. The initial Product Requirements Document is
described in the Binder, under the heading "Product Requirements Document (PRD,
Revision C, dated 06/08/03)," and may be amended from time to time under the
provisions of Section 3 below.

        1.12   Project Management is defined in Section 2.4.1.

        1.13   Resource Plan means the description of (i) a party's personnel to
be allocated to the WNV Development Program, including the name of the specific
personnel or the qualification or grade of unidentified personnel, and dedicated
amount of time and periods for the commitment of such personnel required for the
WNV Development Program, and (ii) equipment, tools, software, or other special
items, the purchase, license or leasing of which is specifically required for
use by such personnel to support the WNV Development Program. The initial
Resource Plan is described in the Binder, under the heading "Resource Plan," and
may be amended from time to time under the provisions of Section 3 below.

        1.14   Software Requirements Specifications (or "SRS") means the
specifications for the software component of the WNV Development Program. The
initial Software Requirements Specifications are described in the Binder, under
the heading "Software Requirements Specifications (SRS, Revision F, dated
06/13/01)," and may be amended from time to time under the provisions of
Section 3 below.

        1.15   Technical Plan means the statement of work prepared for the
development of the WNV Assay Product, including the responsibilities to be
performed by each party, the responsibilities to be performed jointly, the
schedule for performance of those responsibilities, an overall development
timeline and a Resource Plan. The initial Technical Plan is described in the
Binder, under the heading "Technical Plan, Revision B, dated 06/09/03," and may
be amended from time to time under the provisions of Section 3 below.

        1.16   Timeline means the overall development timeline included within
the Technical Plan.

        1.17   WNV Assay Product is defined on Schedule 1.17 and expressly
excludes any products or instruments in the Clinical Diagnostic Field.

        1.18   WNV Development Costs means, with respect to this West Nile Virus
Addendum only, the development costs defined in Section 5 hereof.

        1.19   WNV Development Program means the statement of work for the
development of the WNV Assay Product under the terms of this West Nile Virus
Addendum, as such development program is described in the Binder, and consists
of (i) the Product Requirements Document, (ii) the Software Requirements
Specifications, (iii) the Technical Plan, (iv) the Resource Plan included within
the Technical Plan, and (v) the Budget.

        1.20   WNV Clinical Diagnostic Product means a TMA assay product
developed by Gen-Probe and sold in the Clinical Diagnostic Field to detect the
presence of the West Nile Virus.

        2.    WNV Development Program.    

        2.1    Objective.    Subject to the terms of the Agreement, as amended
by this West Nile Virus Addendum, the parties each shall conduct their
respective obligations under the WNV Development Program as established in
accordance with the terms hereof. The parties acknowledge that, as of the
Addendum Effective Date, the WNV Development Program is a development program
limited to sales of the WNV Assay Product prior to marketing approval by

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the FDA, and further acknowledge that the parties will be required to modify the
WNV Development Program pursuant to Section 3 hereof in the event that the
parties approve a modification to the WNV Development Program designed to result
in marketing approval by the FDA of the WNV Assay Product.

        2.2    General Conduct of Development.    The parties shall conduct
their respective obligations under the WNV Development Program in compliance in
all material respects with all requirements of applicable laws and regulations
and all applicable good laboratory, clinical and manufacturing practices. In
addition, the parties each shall proceed diligently with their respective
obligations under the WNV Development Program and shall use their respective
Commercially Reasonable Efforts to achieve the objectives of the WNV Development
Program efficiently and expeditiously. The parties each shall allocate such
personnel, equipment, facilities and other resources to the WNV Development
Program to carry out their respective obligations and to accomplish the
objectives thereof, all as is more particularly described in the WNV Development
Program, as amended from time to time during the term of this West Nile Virus
Addendum (in accordance with the provisions of Section 3). Each party shall have
the right to consult with the other party regarding the WNV Development Program
and the obligation to reasonably consider the other party's advice.

        2.3    No Guarantee.    While each party agrees to use Commercially
Reasonable Efforts to achieve the objectives described in the WNV Development
Program (as amended from time to time during the term of this West Nile Virus
Addendum (in accordance with the provisions of Section 3) efficiently and
expeditiously, the parties understand that they have embarked on a development
program whose outcome is uncertain. The parties further understand that the WNV
Development Program is subject to a number of variables that are inherent to the
development process and that there is a possibility that the parties may fail to
successfully complete the development of the WNV Assay Product, even though each
party exercises Commercially Reasonable Efforts and commits the resources
described in the WNV Development Program. Neither party will be in breach of its
obligations to the other hereunder and such party shall be deemed to have
exercised Commercially Reasonable Efforts, so long as such party shall have
committed the resources described in the WNV Development Program, even if such
resources fail to successfully complete the development of the WNV Assay
Product, or to complete the development of the WNV Assay Product in accordance
with the Timeline or for the amounts described in the Budget or to the
specifications set forth in the PRD or the SRS. The payment of WNV Development
Costs between the parties shall be due and payable without respect to the
achievement of any particular deliverable specified in the WNV Development
Program.

        2.4    Project Management.    

        2.4.1.    Principles of Project Management.    The parties agree that in
the process of exercising their responsibilities, the Project Management
(consisting of the Project Manager and Project Leaders, as set forth herein)
should have routine access to such information needed to assess progress under
and costs of the WNV Development Program. Specifically, the parties agree that
the Project Leaders shall be invited to participate in all team meetings, and
will have access to team meeting minutes, Timecards and other expense records,
except to the extent the Project Leader for the party assigned principal
responsibility under Section 2.5.3 of this West Nile Virus Addendum for an
activity determines in its reasonable discretion that any such meetings or
minutes contain confidential, proprietary information of the responsible party.
In such cases, the Project Manager shall (i) determine whether the Project
Leader for the party not having primary responsibility for the activity can
attend all or a portion of such meeting, (ii) provide a copy of the meeting
minutes to the Project Leader not having primary responsibility for the activity
with such confidential, proprietary information redacted, and (iii) to the
extent that such minutes had proprietary or confidential

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information redacted, inform the Project Leader not having primary
responsibility of the general nature of any decisions made at such meeting which
affect the Timeline, Budget or Interim Events; provided, however that the
Project Manager may only redact information comprising Gen-Probe intellectual
property and know how or confidential business issues. Project Leaders will have
access to non-confidential and non-proprietary information of the other party
necessary to perform their responsibilities under the WNV Development Program,
including those listed under Section 2.4.4. Project Leaders will inform and
coordinate all activities, including meetings with personnel involved in the
performance of the WNV Development Program, with the Project Manager. The
primary point of contact for the WNV Development Program at Gen-Probe will be
Gen-Probe's Project Manager, the primary point of contact at Chiron will be
Chiron's Project Leader. In order to maintain an efficient and orderly
development the parties will communicate through the primary points of contact
as much as possible when requesting information concerning the progress of the
WNV Development Program. Confidentiality will be maintained in accordance with
Section 8.1 of the Agreement, and disclosure of any information under this
Section 2.4.1 shall be governed by that certain Confidentiality and Joint
Interest Agreement, by and between the parties, dated as of October 30, 2001.

        2.4.2.    Project Manager.    The project associated with development of
the WNV Assay Product will be managed under a Project Manager, the
responsibilities of which are described in Section 2.4.3. The WNV Development
Program will be managed by a Project Manager appointed by Gen-Probe. As of the
Addendum Effective Date, the Project Manager shall be [***]. Any change by
Gen-Probe of the Project Manager must be approved by the Supervisory Board,
which approval shall not be unreasonably withheld.

        2.4.3.    Project Manager's Responsibilities.    The Project Manager
shall be responsible for the following activities, together with such other
activities as the parties may agree:

        (a)   Managing all matters relating to the WNV Development Program under
this West Nile Virus Addendum, including each party's respective
responsibilities and contributions and receiving reports from the Project
Leaders;

        (b)   Providing written monthly progress reports to the parties and
presenting status reports to the Supervisory Board in accordance with
Section 2.4.6 below;

        (c)   Submitting and receiving the reports, materials and documents
required to be delivered under this West Nile Virus Addendum;

        (d)   Overseeing the process of proposing, and submitting to the
parties, any proposed modifications to the Product Requirements Document,
Software Requirement Specifications, Technical Plan, Resource Plan or Budget,
and in the event the parties cannot agree, presenting the same to the
Supervisory Board in an objective and neutral manner;

        (e)   Arranging any meetings to be held between the parties and
participating, to the extent the Project Manager deems appropriate, in meetings
of the Project Leaders;

        (f)    Maintaining, for record keeping purposes, a log book or notes
containing summaries and dates of all material communications and deliveries
between the parties of which the Project Manager is aware, consistent with the
parties' protocol for such sharing of confidential information set forth in that
certain Confidentiality and Joint Interest Agreement, by and between the
parties, dated as of October 30, 2001;

        (g)   Implementing appropriate practices and procedures to manage the
progress under this West Nile Virus Addendum;

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        (h)   Fostering good communication between the parties. It is intended
by the parties that both parties share, through reports from the Project Leaders
to the Project Manager, in the information concerning the progress made in the
WNV Development Program and the cause of any delays. It is expected that the
Project Leaders will make recommendations to the Project Manager for preferred
paths when substantial delays are identified and multiple paths forward are
identified. Understanding that it takes time for information to flow up the
chain of command, the Project Manager will inform Chiron of delays and progress
on resolution as soon as it becomes available to him; and

        (i)    It is understood that both companies hold proprietary trade
secret know-how and processes regarding their respective technologies that are
not necessarily shared as part of this Agreement. On occasion it may occur that
a full understanding of difficulties in the progress of development may require
a detailed understanding of this proprietary know-how and processes. Each party
will endeavor to appraise the other of the outcomes and consequences of these
difficulties, while protecting the confidentiality of the information.

        2.4.4.    Project Leaders.    Gen-Probe and Chiron will each appoint a
project leader (each a "Project Leader") who is responsible for (a) assembling
project teams for his or her respective party and (b) completing project
responsibilities allocated to such party in Section 2.5. For the purposes of
completing the WNV Development Program, these Project Leaders will report to the
Project Manager. The Project Leader employed by a party shall be responsible for
reporting to the employing party whether he or she believes the other party has
proceeded diligently with its stated obligations under the WNV Development
Program, has allocated sufficient personnel, equipment, facilities and other
resources to achieve the objectives of the WNV Development Program and has
exercised Commercially Reasonable Efforts to achieve its objectives efficiently
and expeditiously.

        2.4.5.    Reports.    In addition to the records and reports required to
be kept by the parties under Section 3.5 of the Agreement, each Project Leader
will provide to the Project Manager, in writing, a progress report delivered on
or before the 15th day of each calendar month during the term of the WNV
Development Program. These reports will cover technical progress as well as
financial expenditures and FTE Labor hour reconciliations. The Project Manager
may rely on any such reports for the purpose of making his or her progress
report to the Supervisory Board described in Section 2.4.6 below.

        2.4.6.    Meetings of the Supervisory Board.    The Supervisory Board
shall meet from time to time during the term of this West Nile Virus Addendum,
but not less frequently than once each calendar quarter during the term hereof.
Not less frequently than quarterly, a regular agenda item at the regularly
scheduled Supervisory Board meeting shall be to receive a report from the
Project Manager and conduct a review of the WNV Development Program to assess
progress of the development and the potential for commercialization of the WNV
Assay Product.

        2.5    Development Responsibilities.    

        2.5.1.    Principal Responsibility; General Statement.    The parties'
intention is the smooth and efficient conduct of development, and the parties
desire by this Section 2.5 to provide guiding principles by which day-to-day
decisions may be made by the responsible party and by which the approval process
more particularly described in Section 3 below shall be governed. The parties
intend that portions of the WNV Assay Product development will be conducted
primarily and principally by one or the other of the parties, after consultation
and discussion with the other party, under the supervision of the Project
Manager, as follows: (i) [***]; and (ii) [***]. The party to whom principal
responsibility is allocated in this Section 2.5 has the power to make day-to-day
decisions regarding matters within the area of such responsibility, consistent
with the overall WNV Development Program. The parties' obligations with respect
to certain warehousing and shipping are subject to Amendment No. 3.

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        2.5.2.    Shared Responsibility.    Gen-Probe and Chiron have entered
into that certain Definitive Written Settlement Agreement, dated December 5,
2001. Section 2(a) of the Definitive Written Settlement Agreement incorporates
by reference the provisions of the Short Form Agreement (attached as Exhibit A
to the Definitive Written Settlement Agreement). The parties hereby expressly
incorporate the provisions of Sections F.5 and F.6 of the Short Form Agreement
between the parties, dated November 16, 2001, into this West Nile Virus
Addendum, and agree that the provisions of Sections F.5 and F.6 of the Short
Form Agreement will govern the relationship between the parties for the purpose
of the WNV Assay Product in connection with the subject matters addressed in
those provisions.

        2.5.3.    Principal and Shared Responsibility; Specific
Allocation.    Without limiting the general statements set forth in Sections
2.5.1 and 2.5.2, the parties agree to allocate specific responsibility as
follows:

Function

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  Principal Responsibility

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  Shared Responsibility

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[***]   [***]     [***]   [***]     [***]   [***]     [***]   [***]     [***]  
[***]     [***]   [***]     [***]   [***]     [***]   [***]     [***]   [***]  
  [***]   [***]     [***]   [***]     [***]   [***]     [***]   [***]     [***]
  [***]     [***]       [***] [***]       [***] [***]   [***]     [***]      
[***] [***]   [***]     [***]       [***] [***]   [***]     [***]   [***]    
[***]   [***]     [***]   [***]     [***]   [***]     [***]   [***]     [***]  
    [***]

--------------------------------------------------------------------------------

*Chiron shall have reasonable input into [***].

        2.5.4.    Regulatory/Licensure.    Pursuant to [***].

        2.5.5.    Project Leader Disagreements.    It is recognized that the
Project Leaders may disagree on approaches. Even though one party has the
principal responsibility for development in the functional area described in
Section 2.5, disagreements that cannot be resolved by Project Management may be
brought to the Supervisory Board. However, work will proceed in accordance with
the choice of the principally responsible party, while being

7

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discussed at the Supervisory Board. In the event that the parties do not agree
at the Supervisory Board level, the party with principal responsibility may
continue to proceed per its best judgment. If a disagreement arises in a
functional area for which responsibility is shared and resolution cannot be
achieved at the Supervisory Board, except as to Regulatory/Licensure Strategy
which shall be governed by Section 2.5.4 above, work shall be suspended in such
functional area until a resolution is reached through Article 13 of the
Agreement, including arbitration.

        3.    Modifications.    

        3.1    WNV Development Program Definition.    The parties have prepared
and agreed upon a WNV Development Program, as described in the Binder. The WNV
Development Program, as described in the Binder, will govern the rights and
responsibilities of the parties until changed in accordance with the provisions
hereof. The parties recognize and anticipate that additional clarification and
refinement of the WNV Development Program, including changes, if any, necessary
to reflect accepted delays in, or increases in costs of, development, will be
required as development proceeds. The parties intend that this West Nile Virus
Addendum establish a process by which the parties will amend the WNV Development
Program, in accordance with the terms described in this Section 3.

        3.2    Modifications.    

        3.2.1.    Request for Modifications.    Either party may propose either
Material or Non-material Modifications to any part of the WNV Development
Program from time to time during the term of this West Nile Virus Addendum,
including without limitation a request for a change to the FTE Labor Rate, as
defined in Section 5.2.1. The process applicable to any such proposed
modifications shall be as described in this Section 3. Changes, modifications or
improvements to the WNV Assay Product, after the Completion Date, are governed
by the provisions of Section 4 below. The Project Manager, and under his or her
supervision, the Project Leaders and their respective teams, will review any
proposed modification to the WNV Development Program; if the two Project Leaders
mutually agree in writing that a particular modification is a Material
Modification or is a Non-material Modification, then such determination shall be
conclusive. Unless the two Project Leaders determine to the contrary, any one or
more of the following modifications shall be deemed to be a Material
Modification: a modification that (i) reflects an increase in the actual WNV
Development Costs incurred that, when aggregated with all previously authorized
modifications, is greater than [***] over the Development Costs reflected in the
original Budget approved as of the Addendum Effective Date, or (ii) contains a
proposal to alter any Interim Event as compared to the most recently approved
Timeline, or (iii) contains a proposal to submit a BLA in the United States for
approval from the FDA, or (iv) increases the sales forecast of the WNV Assay
Product to greater than [***] of the WNV Assay Product per month for [***]. If
the Project Leaders are unable to agree whether a particular requested
modification is a Material or Non-material Modification, then the Supervisory
Board shall review the requested change and make a determination with respect to
whether such requested modification is a Material or Non-material Modification.
If the Supervisory Board has met and consulted without resolution, then either
party may, in its discretion, determine that the parties have reached an impasse
with respect thereto and implement the escalation procedure described in
Article 13 of the Agreement to resolve such impasse.

        3.2.2.    Non-Material Modifications.    Unless changes to the
specifications described in Section 3.2.1 constitute a Material Modification,
any Non-Material Modifications shall be reported in the monthly summary progress
reports pursuant to Section 2.4.4 and shall not be subject to the approval
process described in Section 3.3.

8

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        3.3    Material Modifications.    

        3.3.1.    Request for Material Modifications.    In the event that one
party desires to request a Material Modification to the WNV Development Program
from time to time during the term hereof, such party (the "requesting party")
shall submit to the other party such request in writing, in sufficient detail to
enable the other party (the "receiving party") to evaluate the request. Without
limiting the foregoing, the requesting party shall prepare a revised draft
version of the Budget, reflecting any changes necessary to fully implement the
requested Material Modification to the WNV Development Program.

        3.3.2.    Initial Analysis of Impact of Proposed Material
Modification.    Promptly upon receipt of such request, but in any event not
more than [***] thereafter, the parties shall conduct a preliminary analysis of
the impact that the requested Material Modification would have, including
without limitation the impact any such proposed Material Modification would have
on the Budget and/or the Timeline, and shall meet and conduct an analysis of the
impact of such Material Modification on the potential profitability of the WNV
Assay Product. Should either party conclude, in its reasonable discretion, that
the potential for [***] by any proposed change to the WNV Development Program
requested in accordance with this Section 3.3, such party may elect to terminate
participation in the WNV Development Program under the provisions of
Section 8.3.

        3.3.3.    Preparation of Modified WNV Development Program.    Unless the
parties terminate the WNV Development Program for convenience under Section 8.2
below or a party terminates on unilateral withdrawal under Section 8.3 below,
promptly upon completion of the review and analysis under Section 3.3.2,
Gen-Probe and Chiron shall complete and deliver to the Supervisory Board
revisions to the Product Requirements Document, Software Requirements
Specification, Technical Plan, Resource Plan or Budget, as applicable,
responsive to the request for acceptance by the parties under Section 3.3.4
below. Costs incurred by Gen-Probe and Chiron to prepare such response to the
request shall be included in WNV Development Costs hereunder.

        3.3.4.    Acceptance of Modified WNV Development Program.    

        (a)   Unless the parties terminate the WNV Development Program for
convenience under Section 8.2 below or a party terminates on unilateral
withdrawal under Section 8.3 below, the parties shall promptly, but not later
than [***] after preparation by the parties of a modified WNV Development
Program under Section 3.3.3 meet and consult with respect to the proposed
modified WNV Development Program. Either party may elect to terminate
participation in the WNV Development Program under the provisions of Section 8.3
below if the requested modification is a Material Modification, determined in
accordance with Section 3.2.1. If neither party terminates under Sections 8.2 or
8.3 below, then neither party may unreasonably withhold approval of any request
for modification of the WNV Development Program.

        (b)   If neither party terminates under Sections 8.2 or 8.3 below, then
the parties shall thereafter finalize such modified WNV Development Program,
using the provisions of this Section 3.3.4(b), as follows:

          (i)  Each party shall, within [***] following completion of the
consultation and review under paragraph (a), deliver to the other party either a
written approval of the proposed modified WNV Development Program or a detailed
written statement specifying the basis for rejection. Approval shall not be
unreasonably withheld. The requesting party may, in response to a rejection,
revise the proposed modified WNV Development Program to reflect the discussions
of the parties, and redeliver the

9

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revised proposed modified WNV Development Program for further review, until the
parties agree upon the Material Modification. Either party may, in its
discretion and with notice to the other party, determine that the parties have
reached an impasse with respect to any proposed Material Modification and
deliver the request to the Supervisory Board for determination.

         (ii)  If a party delivers the request to the Supervisory Board for
determination, the Supervisory Board shall promptly, but not later than the
later of (i) [***] of a requested modified WNV Development Program, or (ii) the
[***], meet and discuss the proposed Material Modification to WNV Development
Program.

        (iii)  If the Supervisory Board has met and consulted without
resolution, then either party may, in its discretion, determine that the parties
have reached an impasse with respect to any proposed modification and implement
the escalation procedure described in Article 13 of the Agreement to resolve
such impasse. Notwithstanding anything to the contrary in this West Nile Virus
Addendum or the Agreement, all Material Modifications, whether agreed or
determined through arbitration, shall be finally determined and documented in
accordance with this Section 3.3. Where one party has rejected a proposed
modified WNV Development Program, the sole question to be presented in any
arbitration is whether that party unreasonably withheld its approval.

        3.3.5.    Effective Date of Modified WNV Development Program.    At such
time as the parties (or, if applicable, the Supervisory Board) shall have
accepted a modified WNV Development Program incorporating a Material
Modification, or any portion thereof, the parties shall evidence such agreement
by initialing the revised Product Requirements Document, Software Requirements
Specification, Technical Plan, Resource Plan or Budget, as applicable. The WNV
Development Program as so modified and approved shall constitute the WNV
Development Program hereunder and be incorporated by reference into this West
Nile Virus Addendum, and shall supersede the preceding WNV Development Program,
or applicable portions thereof, for all purposes. In order to evidence their
agreement to the revised WNV Development Program, the parties shall include it
in an additional volume of the Binder, labeled "Amendments to WNV Development
Program," in which all amendments and modifications to the WNV Development
Program will be kept.

        3.4    Notice of Significant Changes.    Each party will give [***]
notice to the other party prior to any proposal of a significant reduction or
increase in resources from the then-current Resource Plan in order to allow the
parties time to divert resources either to or from the WNV Development Program.
Any significant changes to the Budget or the Resource Plan shall be effective
only upon the expiration of [***] from the delivery of such notice, unless the
parties both agree to a shorter period of time in writing.

        4.    Changes to WNV Assay Product after Completion Date.    

        4.1    Process.    Notwithstanding the provisions of Section 3, the
parties recognize that from time to time during the term hereof the market may
demand or regulatory changes may require that special enhancements or
modifications be made to the WNV Assay Product, and that either party may desire
to adopt such changes. From and after the Completion Date, each party will
notify the Supervisory Board promptly upon receipt of a request from a customer,
or upon identification of regulatory changes that may require the parties to
implement any enhancement, modification or other change to the WNV Assay
Product. The Supervisory Board shall promptly, but not later than the latter of
(i) [***] for such changes to the WNV Assay Product, or (ii) [***], meet and
consult with respect to such requested change. The Supervisory Board shall
decide (i) whether the requested changes should be implemented; and (ii) whether
the requested changes

10

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can be implemented under the terms of this West Nile Virus Addendum or are
significant enough to warrant a new Development Program under the terms of
Article 3 of the Agreement, in which case the parties shall use the process more
particularly described in Section 3.2 of the Agreement.

        4.2    Additional Work under Addendum.    If the Supervisory Board
determines that the changes are sufficiently minor that they can be implemented
under this West Nile Virus Addendum, then the parties shall implement the
process more particularly described in Section 3.3 above, and the Supervisory
Board may approve a new WNV Development Program, consisting of a new modified
Product Requirements Document, Software Requirements Specifications, Technical
Plan, Resource Plan and Budget, for the purpose of developing such changes.
Notwithstanding the foregoing, nothing herein shall obligate either party to
conduct development work after the Completion Date with respect to the WNV Assay
Product, without regard to whether the other party indicates a willingness to
pay some portion or the entire costs of such development.

        5.    WNV Development Costs.    

        5.1    [***] WNV Development Costs.    Each party is responsible for and
agrees to pay [***], which WNV Development Costs included within the original
WNV Development Program Budget as of the Addendum Effective Date are attached as
Schedule 1.4A and Schedule 1.4B. The Budget has been prepared for the purpose of
permitting the parties to plan for WNV Development Program expenditures related
to WNV Development Costs hereunder and represents the parties' best estimate of
such WNV Development Costs, but does not represent a "fixed price maximum" or
other guaranteed maximum cost of the development required for the WNV
Development Program.

        5.1.1.    [***].    Gen-Probe shall be solely entitled to the benefit
of, and be solely responsible for the application and accounting of, any [***].
Notwithstanding anything to the contrary herein, Gen-Probe shall not be
obligated to pay to Chiron, or credit against WNV Development Costs, any [***]
received by Gen-Probe relating to development of the WNV Assay Product or to the
WNV Development Program.

        5.1.2.    Prior to Material Modification.    Before the effective date
on which a Material Modification is approved in accordance with the provisions
of Section 3, WNV Development Costs included within the original WNV Development
Program Budget approved as of the Addendum Effective Date shall be reimbursed
under this Section 5.1.2. In addition, this Section 5.1.2 is in lieu of the
distribution of Net Sales as described under the Agreement, including the
provisions of Section 3.2.7(a) and (b). Attached hereto as Schedule 1.4A and as
Schedule 1.4B are the WNV Development Costs for Gen-Probe and Chiron,
respectively, approved by the Supervisory Board as of the Addendum Effective
Date. The reimbursement of WNV Development Costs under this Section 5.1.2 shall
be solely from Net Sales. Neither party shall be obligated to reimburse the
other for WNV Development Costs reflected on Schedule 1.4A and Schedule 1.4B
from sources other than Net Sales under this Section 5.1.2. Based on the
relative WNV Development Costs expended by each party, as reflected on
Schedule 1.4A and Schedule 1.4B, and based on an amortization of such costs over
a [***] period, the parties have agreed that Net Sales (as defined in this
Section 5.1.2) from the sale of the WNV Assay Product before the effective date
on which a Material Modification is approved shall be shared [***] to Gen-Probe
and [***] to Chiron. Within [***] of receipt of revenue from the sale of the WNV
Assay Product, Chiron shall calculate Net Sales (as defined in this
Section 5.1.2), provide Gen-Probe with written notice of such calculation and
pay Gen-Probe [***] of Net Sales (as defined in this Section 5.1.2).
Notwithstanding Section 1.46 of the Agreement, and solely for the purpose of
calculating Net Sales under this Section 5.1.2, Net Sales means [***], without
any deduction or offset of any kind, other than

11

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for [***] payments made to Gen-Probe previously for WNV Assay Product, if any,
used to perform the testing.. (The parties agree that, as of the Addendum
Effective Date, [***]).

        5.1.3.    After Material Modification.    From and after the effective
date on which a Material Modification is approved in accordance with the
provisions of Section 3, WNV Development Costs shall be paid as follows:

        (a)   The Supervisory Board may decide that WNV Development Costs
(consisting of both the WNV Development Costs reflected on Schedule 1.4A and
Schedule 1.4B and the additional WNV Development Costs approved in connection
with the approval of the applicable Material Modification) shall continue to be
reimbursed solely from Net Sales as defined in and using the methodology
described in Section 5.1.2. In such event, the Suprevisory Board shall evaluate
the relative additional WNV Development Costs expended by each party, as
reflected in the Material Modification, and, based on an amortization of such
costs over a [***] period, determine a new percentage reimbursement from the
percentage reimbursement described in Section 5.1.2.

        (b)   If the Supervisory Board has not made the decision described in
Section 5.1.3(a) above, then the additional WNV Development Costs approved in
connection with the approval of the applicable Material Modification (in excess
of the WNV Development Costs reflected on Schedule 1.4A and Schedule 1.4B) shall
be paid using the process described in Sections 5.2 and 5.3 herein. The
remaining provisions for the distribution of Net Sales as described under the
Agreement, including the provisions of Section 3.2.7(a) and (b) shall apply to
such sales.

        5.2    Definition and Calculation of WNV Development Costs.    WNV
Development Cost" with respect to the WNV Development Program means the
fully-burdened cost of conducting the research and development (including
clinical trials and domestic and international regulatory submissions) of the
WNV Assay Product, and shall include (i) the reasonable cost of all quantities
of raw materials, intermediates and finished goods necessary for the manufacture
of such quantities of the WNV Assay Product utilized during the WNV Development
Program, and (ii) the reasonable cost of such quantities of the WNV Assay
Product that are manufactured for, but not utilized during, the WNV Development
Program, that are not sold nor retained for research and/or development or other
internal purpose and are scrapped due to product expiration. Costs will be
calculated in accordance with United States generally accepted accounting
principles, consistently applied ("U.S. GAAP"), or as otherwise mutually agreed
in writing between the parties.

        5.2.1.    WNV Development Costs; FTE Labor Rate.    

        (a)   In lieu of accounting specifically for and receiving direct
reimbursement for certain WNV Development Costs, the parties have agreed to
include reimbursement for those certain categories of WNV Development Costs
within an agreed-upon labor rate for full time equivalent personnel (the "FTE
Labor Rate"). Those categories of "WNV Development Costs" included within the
FTE Labor Rate are those costs more particularly described on Schedule 5, in
paragraph 2 entitled "WNV Development Costs included within FTE Labor Rate".
Neither party shall be reimbursed separately for WNV Development Costs included
within FTE Labor Rate. Those categories of "WNV Development Costs" not included
within the FTE Labor Rate are those costs more particularly described on
Schedule 5, in paragraph 3 entitled "WNV Development Costs not included within
FTE Labor Rate". Each party shall be reimbursed separately for WNV Development
Costs not included within FTE Labor Rate.

12

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        (b)   The FTE Labor Rate in effect as of the Addendum Effective Date is
set forth in paragraph 1 on the attached Schedule 5, and is included in the
Resource Plan and reflected in the Budget. Each year the parties will evaluate
and re-set a FTE Labor Rate for the Budget for the new calendar year based on
the parties' budgets for the then-current calendar year and consistent with the
requirements of Section 5.2.1(d) below. In the event the parties shall not have
agreed upon a new FTE Labor Rate before commencement of a calendar year, the
parties shall use the rate in effect during the immediately preceding calendar
year for billing purposes, subject to "true-up" (using the same methodology as
described in Section 5.2.1(e) below) at such time as the FTE Labor Rate for the
then-current calendar year has been agreed.

        (c)   In addition to the annual reset described in Section 5.2.1(b)
above, either party shall have the right to request a change in the FTE Labor
Rate reflected on the attached Schedule 5 to be applied on a prospective basis
under the approval process set forth in Section 3. Acceptance of such request
for modification shall be governed by Section 3.3.4 of this West Nile Virus
Addendum.

        (d)   In addition to the foregoing, throughout the term of this West
Nile Virus Addendum:

          (i)  each party shall have the same FTE Labor Rate applicable to it as
is applied to the other party, subject to any agreed modifications; and

         (ii)  in the event either party requests a modification to the FTE
Labor Rate hereunder, the modified FTE Labor Rate shall be calculated using the
same methodology as that used to calculate the FTE Labor Rate in effect as of
the Addendum Effective Date. The methodology used to calculate the FTE Labor
Rate in effect as of the Addendum Effective Date is described on the attached
Schedule 5.2.3, entitled "WNV Development Costs Calculation Methodology".

        (e)   In the event aggregate actual WNV Development Costs that are
reimbursed through the FTE Labor Rate exceeded, or fell short of, the agreed FTE
Labor Rate reflected in the Budget (as agreed to in accordance with the
provisions of Section 5.2.1(b) above) for such calendar year, the parties will
"true-up" such reimbursement annually in accordance with this Section 5.2.1(e).
[***] during the term hereof, each Gen-Probe will calculate and deliver to
Chiron an accounting of the actual expenditures made by Gen-Probe for those
costs more particularly described on Schedule 5, in paragraph 2 entitled "WNV
Development Costs included within FTE Labor Rate" and compare them to the
amounts reimbursed through the FTE Labor Rate in such year. Each party will have
[***] in which to meet and agree upon a final FTE Labor Rate for such year (the
"Final FTE Labor Rate") which more closely approximates the actual labor rate
experienced by each party. If necessary Chiron will travel to Gen-Probe in order
to complete the review in these timeframes. Each party shall have the same Final
FTE Labor Rate applicable to it as is applied to the other party, subject to any
agreed modifications. If the parties disagree on a Final FTE Labor Rate, such
disagreement shall be addressed by the Supervisory Board and, if necessary, by
implementation of the escalation procedure described in Article 13 of the
Agreement, excluding arbitration. In the event that one party received less than
the Final FTE Labor Rate, such party shall be entitled to receive from the other
party an amount equal to [***] of the difference between the actual WNV
Development Costs included within the FTE Labor Rate and the reimbursed WNV
Development Costs included within the FTE Labor Rate; similarly, in the event
that one party received more than the Final FTE Labor Rate, such party shall be
required to reimburse the other party in an amount equal to [***] of the

13

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difference between the actual WNV Development Costs included within the FTE
Labor Rate and the reimbursed WNV Development Costs included within the FTE
Labor Rate.

        (f)    WNV Development Costs not included within the FTE Labor Rate
shall be budgeted and trued-up under the same terms as the FTE Labor Rate.

        5.2.2.    Comparison with Resource Plan.    The planned resources, and
the associated costs, will be broken out on a monthly basis and analyzed against
the Resource Plan included within the Technical Plan, and reflected in the
Budget.

        5.2.3.    Methodology.    Attached hereto as Schedule 5.2.3 is a
detailed methodology for the calculation of the WNV Development Costs, including
costs reimbursed through the FTE Labor rate and significant external costs, as
defined in this Section 5.2. The parties shall use such methodology for the
purpose of invoicing and payment more particularly described in Section 5.3
below.

        5.3    Payment of WNV Development Costs.    In addition to the
provisions of Article 7 of the Agreement, the parties agree as follows:

        5.3.1.    Accrued WNV Development Costs.    Each party has already
incurred, prior to the date of execution of this West Nile Virus Addendum,
certain WNV Development Costs. To the extent that one party has paid more than
its [***] share of the aggregate WNV Development Costs incurred prior to and
until the date of execution of this West Nile Virus Addendum, the other party
will reimburse such party for [***] the WNV Development Costs paid by that party
and [***] of the aggregate WNV Development Costs incurred prior to and until the
date of execution of this West Nile Virus Addendum. Attached to this West Nile
Virus Addendum as Schedule 5.3.1 is a summary of the WNV Development Costs
incurred by the parties prior to the execution of this West Nile Virus Addendum.

        5.3.2.    [***] Budgeted Payments.    Each party's respective [***]
share of WNV Development Costs will be paid on a [***] in an amount equal to the
amount reflected in Budget for that particular [***]. The Budget sets forth the
parties' anticipated expenditures and FTE Labor amounts for WNV Development
Costs for [***] during the term of the WNV Development Program in the line item
entitled "Total Project GP" and "Total Project Chiron," respectively. The line
items entitled "GP Payment to Chiron" and "Chiron Payment to GP" in the Budget
identify (i) the amount by which Chiron and Gen-Probe, respectively, are
anticipated to incur WNV Development Costs in excess of their respective [***]
share (the "negative delta"), and (ii) the party who is required to make the
reimbursement payment. [***] during the term of the WNV Development Program,
Gen-Probe will invoice Chiron the amount of such negative delta net of any
credits or additional charges against amounts previously paid that have been
agreed to by the Project Management prior to the date on which Gen-Probe
rendered the invoice. Attached hereto as Schedule 5.3.2 is an example of this
payment methodology.

        5.3.3.    [***] True-Up Payments.    At the end of each [***], each
party will calculate the actual FTE Labor hours expended on the WNV Development
Program during such [***]. The Project Leaders will review these actual FTE
Labor hours compare them to the Budget for the applicable [***]. In the event
that one party expended more than [***] share of actual FTE Labor hours or WNV
Development Costs not included in the FTE Labor hours during the [***] then
ended, taking into account all payments made under Section 5.3.2, the parties
shall calculate the cost of such negative delta using the agreed FTE Labor Rate
and Gen-Probe will adjust the next invoice issued to Chiron in the amount of
such credit or additional charge on or before the expiration of [***] after the
end of the applicable [***]. Attached hereto as Schedule 5.3.3 is an example of
this true-up methodology.

14

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        5.3.4.    Invoices.    Each party will invoice the other for the amounts
described in this Section 5.3 and all invoices will be due and payable [***]
from the date of the invoice. In the event payment is not received within such
period, the delinquent party shall pay a service charge if billed, equal to the
amount overdue multiplied by the [***], but not exceeding the maximum allowable
rate.

        5.4    Additional Provisions regarding Shared Revenues.    

        5.4.1.    [***].    In addition to the provisions of Section 5.3 of this
Addendum to the Agreement, within [***] following the [***], Gen-Probe shall pay
to Chiron [***]. Gen-Probe's obligation under this Section 5.4 shall be
Gen-Probe's sole and exclusive obligation to Chiron with respect to sale of the
[***].

        5.4.2.    [***].    In addition to the provisions of Section 5.3 of this
Addendum to the Agreement, within [***] following the [***], Chiron shall pay to
Gen-Probe [***]. Chiron's obligation under this Section 5.4 shall be Chiron's
sole and exclusive obligation to Gen-Probe with respect to sale or licensing of
the [***].

        5.5    Dispute.    Neither party shall unilaterally invoice the other in
advance for more than the amount reflected in the then-current Budget in a given
period nor withhold payments of the amount reflected in the then-current Budget.
Either party may, in its discretion, determine that the parties have reached an
impasse with respect to a particular Budget item, the invoicing or payment of
same, and implement the escalation procedure described in Article 13 of the
Agreement to resolve such impasse. Notwithstanding the foregoing, neither party
may withhold payment of [***] budgeted payments under Section 5.3.2, cease
development work or otherwise impede the progress of the WNV Development Program
by reason of such dispute.

        5.6    Right to Audit and Verify.    Each party is entitled to review,
evaluate, and in its discretion independently verify the basis of and actual
expenditures incurred by the other party for which such party requests
reimbursement as WNV Development Costs hereunder, in accordance with the
provisions of Section 7.3 of the Agreement, including without limitation actual
expenditures after the Addendum Effective Date but prior to the execution of
this West Nile Virus Addendum, if applicable.

        6.    Manufacturing and Commercialization.    

        6.1    Definitions Relevant to Manufacturing and Commercialization
Obligation.    The parties intend that the WNV Assay Product falls within the
following provisions of the Agreement:

        6.1.1.    Applicable Purchase Price.    As used in the Agreement, the
"Applicable Purchase Price" applicable to the WNV Assay Product is as set forth
in Section 1.2.3 of the Agreement. The parties acknowledge that the WNV Assay
Product is a Future Blood Screening Assay which does not include as a
constituent element an assay for HCV, for which the provisions of Section 1.2.3
of the Agreement describes the "Applicable Purchase Price", as determined from
time to time during the term of the Agreement. Notwithstanding section 3.2.7(b)
of the Agreement, the Applicable Purchase Price for the WNV Assay Product in the
Territory will never be less than [***].

15

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        6.1.2.    Transfer Price.    

        (a)   At each sale of the WNV Assay Product sold as an IUO product, the
"Transfer Price "applicable to (i) so much of the WNV Assay Product as consists
of the West Nile Virus assay specific reagents is [***] and (ii) so much of the
WNV Assay Product as consists of the reagents in common with other approved
Blood Screening Assays is the Transfer Price established in accordance with
Section 1.58. of the Agreement. Where the Transfer Price is [***], Chiron will
issue purchase orders at [***] to Gen-Probe for WNV specific assay reagents, and
Gen-Probe will transfer them to Chiron.

        (b)   At such time as Section 5.1.3(b) applies, the "Transfer Price"
applicable to the WNV Assay Product is set forth in Section 1.58.2 of the
Agreement, except that the Transfer Price for WNV Assay Product from conformance
or development lots that is transferred to Third Parties in the Territory for
use in the Blood Screening Field shall reflect and be adjusted if and to the
extent that the costs of manufacture of such conformance or development lots is
included as part of the WNV Development Costs shared by the parties under
Section 5.

        (c)   In any case, the commercial sale of an IVD-labelled WNV Assay
Product will be governed by the terms of the April 1, 2002 Amendment No. 3
(warehousing and shipping), and the Transfer Price [***]. The second sentence of
Section 1.58.2 is deleted in its entirety, and replaced with the following:

        "The Transfer Price, based on this objective, [***]."

        6.1.3.    Manufacturing Cost.    The "Manufacturing Cost" for the WNV
Assay Product shall be as defined in the Agreement.

        6.1.4.    Rare Reagents.    The WNV Assay Product is a Future Blood
Screening Assay which incorporates substantial Rare Reagents, as defined in
Section 1.51 of the Agreement.

        6.2    Right to Audit and Verify.    Chiron is entitled to review,
evaluate, and in its discretion independently verify the basis of Gen-Probe's
Manufacturing Cost using an independent third party, in accordance with the
provisions of Section 7.3 of the Agreement.

        6.3    Non-Commercial Products.    

        6.3.1.   If any portion of the notebook, development, clinical or
conformance lots of the WNV Assay Product manufactured for the WNV Development
Program is sold to a Third Party for use outside the United States or utilized
by Chiron or Gen-Probe in a research or development program other than the WNV
Development Program, including without limitation research studies or marketing
studies performed in support of commercialization of the WNV Assay Product, or
the development and clinical trials for the Tigris instrument, the party selling
or utilizing such WNV Assay Product shall reimburse the WNV Development Program
to the extent that the program was charged for the materials.

        6.3.2.   Section 6.10 of the Original Agreement is amended to add the
following as new subsection (b), applicable to the WNV Assay Product only:

"(b) Gen-Probe agrees to provide to Chiron reasonable quantities of the WNV
Assay Product manufactured by Gen-Probe for uses other than sale to customers,
including without limitation research studies, marketing studies, internal
research and development, and troubleshooting (all for Chiron's use only in
direct furtherance of the express purposes of this Agreement and without any
implied license for any purpose other than such express purposes), to the extent
such Products are specifically ordered by Chiron for such purposes
("Non-commercial WNV Assay Products"). The entire compensation to

16

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Gen-Probe for Non-commercial Products shall be not greater than [***], as
determined by reference to Gen-Probe's customary and ordinary accounting
practices. The quantities of Non-commercial WNV Assay Products ordered by Chiron
as well as quantities of WNV Assay Products consumed by Gen-Probe for all
purposes other than the West Nile Virus Assay Development Program shall be
subject to review by the Supervisory Board."

        6.4    Commercialization Budget.    

        (a)   For the purpose of determining "commercialization costs" (to be
reimbursed to Chiron as permitted in Section 8.5 of the Agreement), Chiron shall
submit to Gen-Probe a commercialization budget, promptly following any
termination of this West Nile Virus Addendum for breach in accordance with
Section 8.1 or an unilateral withdrawal by a party in accordance with
Section 8.3, and the timely election by a Continuing Party to continue the WNV
Development Program, as described in this Section 6.4.

        (b)   Chiron shall submit to Gen-Probe a commercialization budget,
setting forth the programs and anticipated costs, including applicable costs and
overhead for internal sales, marketing, distribution, training, technical
support, instrument service and field service engineering, product support,
quality assurance, regulatory affairs and clinical affairs all as required to
commercialize the West Nile Virus Assay. Such commercialization budget shall
also include out-of pocket costs associated with each such program and
initiative plus costs associated with any third party support and allocated
costs of instrumentation on a per unit or other reasonable allocation method
applicable to the commercialization of the WNV Assay Product. The detail and
basis provided in the proposed budget shall be commensurate with the information
supplied by Gen-Probe to support Gen-Probe's calculation of Manufacturing Cost.

        (c)   Gen-Probe will deliver to Chiron either a written acceptance of
the proposed commercialization budget or a detailed written statement specifying
the basis for rejection. Chiron may, in response to a rejection, revise the
proposed commercialization budget to reflect the discussions of the parties, and
redeliver the revised commercialization budget for further review, until the
parties agree upon the final commercialization budget. Either party may, in its
discretion and with notice to the other party, determine that the parties have
reached an impasse with respect to the proposed commercialization budget and
deliver a request to the Supervisory Board for determination.

        (d)   If a party delivers the request to the Supervisory Board for
determination of the commercialization budget, the Supervisory Board shall
promptly, but not later than the later of (i) [***], or (ii) the [***], meet and
discuss the proposed commercialization budget.

        (e)   If the Supervisory Board has met and consulted without resolution,
then either party may, in its discretion, determine that the parties have
reached an impasse with respect to the proposed commercialization budget and
implement the escalation procedure described in Article 13 of the Agreement to
resolve such impasse.

        (f)    Labeling: Labeling will indicate that the Product was "Developed
by Gen-Probe, in collaboration with Chiron"

        7.    License Grants.    

        The grant of licenses for the purpose of conducting the WNV Development
Program shall be governed by Sections 3.2.6 and Section 9 of the Agreement. For
the avoidance of doubt, Chiron confirms that Gen-Probe shall be [***].

17

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        8.    Addendum Effective Date; Term; Termination.    

        Term of West Nile Virus Addendum.    This West Nile Virus Addendum shall
become effective on the Addendum Effective Date and shall continue in effect
through the Blood Screening Term, unless sooner terminated in accordance with
the provisions hereof. For the avoidance of doubt, the parties reiterate that
the WNV Assay Product to be developed under this Addendum constitutes a Future
Blood Screening Assay pursuant to the Agreement. Termination of this West Nile
Virus Addendum prior to the expiration of the Blood Screening Term shall be
governed by the terms of this Section and termination of the Agreement shall be
governed by Section 11.2 of the Agreement.

        8.1    Termination for Breach.    

        8.1.1.    Default.    Either party (the "nondefaulting party") has the
right, upon written notice to the other party (the "defaulting party"), to
terminate the WNV Development Program, upon the occurrence of any of the
following events of default and the expiration of any applicable period of time
for cure:

        (a)   if a party fails to make a payment required under Sections 5.3.2
or 5.3.3 hereunder;

        (b)   if a party invoices for amounts using expenditures not falling
within the definition of WNV Development Costs or not included within the
Budget.

        (c)   if a party fails to exercise Commercially Reasonable Efforts to
commit the resources described in the WNV Development Program or to exercise
Commercially Reasonable Efforts achieve the objectives of the WNV Development
Program; provided, however, that the failure to successfully complete the
development of the WNV Assay Product, or to complete the development of the WNV
Assay Product on the Timeline set forth in the Technical Plan or for the amounts
described in the Budget or to the specifications set forth in the PRD or the SRS
shall not be deemed to be a breach of this West Nile Virus Addendum; and

        (d)   if a party defaults under the Agreement which default results in
the termination of the Agreement.

        8.1.2.    Right to Cure Event of Default.    Upon the occurrence of any
event of default entitling a party to terminate this West Nile Virus Addendum,
the non-defaulting party may send notice of event of default, specifying in
reasonable detail the nature of the default, to the defaulting party. The
defaulting party will have [***] following the date of receipt of such notice
within which to cure the breach or event of default. Failure to cure the default
within such time period will result in termination of the WNV Development
Program without further notice by the non-defaulting party, unless such
non-defaulting party extends the cure period by written notice or withdraws the
default notice. (The expiration of the period for such right to cure without
cure, extension or withdrawal of the default notice is referred to as the
"effective date of termination".)

        8.1.3.    Effect of Termination for Breach.    Upon a termination of
this West Nile Virus Addendum for default under this Section 8.1:

        (a)   Subject to the rights of the parties under Section 9.3, the WNV
Development Program shall be terminated.

        (b)   The non-defaulting party's rights under the Agreement shall remain
in full force and effect unchanged.

        (c)   The defaulting party's rights under the Agreement with respect to
all Products, other than the WNV Assay Product, shall remain in full force and
effect unchanged.

18

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        (d)   The defaulting party's rights under the Agreement with respect to
the WNV Assay Product shall terminate and be of no further force and effect. The
defaulting party may not undertake a development substantially similar to the
WNV Development Program with any other party for a period of [***].

        (e)   The defaulting party shall pay, to the other party, in addition to
any other rights or remedies available to the nondefaulting party at law or
equity, promptly upon receipt of an invoice therefore, an amount equal to
(i) [***], (ii) [***].

        8.2    Termination by Both Parties.    

        8.2.1.    Vote to Terminate.    The Supervisory Board, by unanimous
vote, has the right, upon three (3) months written notice to both parties, to
terminate the WNV Development Program and by extension this West Nile Virus
Addendum.

        8.2.2.    Effect of Notice Period on Termination by Both
Parties.    During the notice period as set forth in Section 8.2.1, the
provisions for reimbursement of a party's development efforts in accordance with
the then-current Budget continue in force and effect, unless the party faced
with reduction agrees that it can displace employees to other activities in a
shorter time. The parties agree that each party shall attempt to minimize costs
during the notice period. During the notice period, the parties shall continue
to perform their respective obligations under the WNV Development Program,
unless otherwise agreed by the parties in writing. Upon the expiration of the
notice period (and the effective date of termination under Section 8.1 or the
effective date of withdrawal under Section 8.3 of the WNV Development Program),
each party shall pay, promptly upon receipt of an invoice therefor, to the other
party an amount equal to (i) all WNV Development Costs accrued to date in the
terminated WNV Development Program for which an invoice has been rendered and
(ii) all WNV Development Costs not yet invoiced but incurred in the terminated
WNV Development Program, whether or not disputed, as set forth in the approved
Budget.

        8.2.3.    Effect of Termination by Both Parties.    Upon any termination
of the WNV Development Program under this Section 8.2, the parties shall have
such rights on termination as shall be unanimously agreed by the Supervisory
Board as part of the decision to terminate for convenience.

        8.3    Termination by Either Party; Unilateral Withdrawal from WNV
Development Program.    Either party (referred to for convenience as the
"withdrawing party") may elect to terminate this West Nile Virus Addendum under
this Section 8.3 on the following basis without further cause:

        (a)   The withdrawing party concludes in its reasonable discretion that
the potential for [***] by any proposed change to the WNV Development Program
requested in accordance with Section 3.3 above; or

        (b)   The withdrawing party receives a request for a Material
Modification of the WNV Development Program as determined in accordance with
Section 3.2.1; or

        (c)   The parties have failed to achieve one or more of the Interim
Events.

        The withdrawing party may terminate this West Nile Virus Addendum under
this Section 8.3 upon the provision to the other party (referred to for
convenience as the "non-withdrawing party") of [***], specifying in reasonable
detail the basis on which the withdrawing party is unilaterally terminating this
West Nile Virus Addendum. (The notice of intent to withdraw described in this
Section 8.3 is referred to for convenience as the "withdrawal notice"; and a
date which [***] later is referred to for convenience as the "effective date of
withdrawal").

19

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        8.4    Continuance of WNV Development Program following Unilateral
Withdrawal or Termination.    

        8.4.1.    Election.    Following any termination of this West Nile Virus
Addendum for breach in accordance with Section 8.1 or an unilateral withdrawal
by a party in accordance with Section 8.3, the non-defaulting party (under
Section 8.1) or the non-withdrawing party (under Section 8.3) (referred to for
convenience as the "Continuing Party") may elect to continue the WNV Development
Program by providing written notice to the other party on or before the
effective date of termination under Section 8.1 or the effective date of
withdrawal under Section 8.3.

        8.4.2.    Funding and Conduct of Development.    

        (a)   If a Continuing Party elects pursuant to this Section 8.4 to
continue funding the WNV Development Program, such Continuing Party shall be
solely responsible for the current funding of all WNV Development Costs from and
after the effective date of termination under Section 8.1 or the effective date
of withdrawal under Section 8.3, subject to the right to reimbursement more
particularly described below.

        (b)   In addition to Section 8.4.2(a), if the Continuing Party is
Chiron, Chiron shall pay Gen-Probe [***]. Such amount shall be payable in
accordance with the provisions of [***]. Chiron shall be entitled to
reimbursement of such amounts paid in accordance with the provisions of
Section 8.4.3 below.

        8.4.3.    Reimbursement of Development Costs.    The party electing to
continue development under the terms of Section 8.4 shall be deemed to be the
party who "wishes to develop the Future Blood Screening Assay" described in
Section 3.2.1(c) of the Agreement. The provisions of Section 3.2.1(c) and the
provisions of Section 3.2.3(b)(i) of the Agreement shall govern the rights and
obligations of the parties from and after the effective date of termination
under Section 8.1 or the effective date of withdrawal under Section 8.3 of the
WNV Development Program as a joint development program under this West Nile
Virus Addendum, except Section 3.2.1(b) of the Agreement shall be deleted in its
entirety, and replaced with the following.

        "b. In the case of a Future Blood Screening Product which is funded by
one party pursuant to Section 3.2.1(c) of the Agreement and Section 8.4 of the
West Nile Virus Addendum, such party shall be solely responsible for all
Development Costs of such Future Blood Screening Assay and be entitled to
reimbursement of the portion of the total Development Costs incurred after the
effective date of termination under Section 8.1 or the effective date of
withdrawal under Section 8.3, as the case may be (the "Post-Withdrawal
Development Costs"), as follows:

            i.  If the funding party is Gen-Probe, Chiron shall [***].
Thereafter, Net Sales shall be paid as provided under Section 3.2.7 of the
Agreement.

           ii.  If the funding party is Chiron, Chiron shall pay to Gen-Probe
[***], then Chiron shall [***]. Thereafter, Net Sales shall be paid as provided
under Section 3.2.7 of the Agreement.

          iii.  The parties agree that the funding party is entitled to a
preferential return on the Post-Withdrawal Development Costs incurred by the
funding party, as a reasonable return for the additional risk incurred by the
funding party, in an amount equal to [***] on the Post-Withdrawal Development
Costs actually incurred by the funding party from the date incurred until the
date on which such Post-Withdrawal Development Costs are reimbursed from WNV
Assay Product revenues pursuant to Section 3.2.1(b)(i) above or
Section 3.2.1(b)(ii) above, as applicable."

20

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        8.4.4.    Control of the Program upon Unilateral Funding.    The
Continuing Party shall have the right to appoint the Project Manager from and
after the effective date of termination under Section 8.1 or the effective date
of withdrawal under Section 8.3. The Continuing Party shall have the right to
make such Material Modifications to the WNV Development Program that it deems
necessary or prudent in its reasonable discretion, without the acceptance of the
other party as otherwise required under Section 3.3.4 of this West Nile Virus
Addendum. Notwithstanding the above, the Continuing Party shall remain obligated
to provide the other party with a copy of the WNV Development Program, and all
notice and reporting obligations set forth herein shall remain in full force and
effect.

        8.4.5.    Rights under Agreement.    Except as expressly modified by
this Section 8.4, the parties shall retain all rights and obligations allocated
pursuant to Section 3.2 of the Agreement. Without limiting the foregoing,
without respect to which party is the Continuing Party, Gen-Probe shall have the
exclusive right and obligation to conduct the development work and to
manufacture the WNV Assay Product; Chiron shall have the exclusive right to
promote, market and sell the WNV Assay Product and the parties shall have their
respective rights under Section 3.2.8 of the Agreement, all as is more
particularly described in the Agreement unaffected in any way by the withdrawal
from the WNV Development Program.

        9.    Escalation.    

        9.1    Escalation Process.    Prior to implementing the arbitration
process more particularly described in Article 13 of the Agreement, the parties
agree to escalate any dispute first to a discussion between responsible
managers, and if they cannot agree, then to the Supervisory Board. However the
parties explicitly acknowledge that in the event of the need for an urgent
decision the party with primary responsibility will proceed to make the
decision, and implement. It is agreed that the party with primary responsibility
will make all reasonable and timely efforts to inform the other party of the
issue requiring decision, particularly where the issue is one of some
consequence.

        9.2    Remedies in Event of Default.    Neither party shall be entitled
to exercise any remedy otherwise available to it at law or in equity unless and
until such party shall have provided the other party with notice of such event
of default, reasonably specifying the nature of the default, and any applicable
period of time for cure thereof shall have expired without cure, and the
procedures defined in Article 13 of the Agreement shall have been first
exhausted.

        9.3    Survival.    Upon a termination of this West Nile Virus Addendum,
the following provisions of this West Nile Virus Addendum shall survive such
termination: Sections 2.3, 2.4.1, 7, 8, 9, and 10 and all rights under
Section 5.3.3 that have accrued as of the date of termination.

        10.    No Other Amendment.    Except as expressly set forth in this West
Nile Virus Addendum, all other terms and conditions of the Agreement, the
parties' Definitive Written Settlement Agreement, dated December 5, 2001, and
the Short Form Agreement, dated November 16, 2001, are hereby ratified and shall
continue in full force and effect. In the event of a conflict between the terms
of this West Nile Virus Addendum and the Agreement, the terms of this West Nile
Virus Addendum shall control. The provisions of this West Nile Virus Addendum
are intended to, and hereby, supercede any provisions in the Definitive Written
Settlement Agreement entered into by and between the parties, dated December 5,
2001, and the Short Form Agreement entered into by and between the parties,
dated November 16, 2001, on the same subject matter.

        11.    Counterparts.    This West Nile Virus Addendum may be executed in
counterparts, each of such shall be deemed an original, and all of which
together shall constitute one and same instrument.

21

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        IN WITNESS WHEREOF, the parties have caused this West Nile Virus
Addendum to be executed and the persons signing below warrant that they are duly
authorized to sign for and on behalf of the respective parties.

GEN-PROBE INCORPORATED,
a Delaware corporation   CHIRON CORPORATION,
a Delaware corporation
By:
 
/s/  HANK NORDHOFF      

--------------------------------------------------------------------------------

 
By:
 
/s/  JACK GOLDSTEIN      

--------------------------------------------------------------------------------

Its:   President; CEO   Its:   President, CBT Date:   Oct. 21, 2003   Date:  
Oct. 10, 2003

22

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Schedule 1.4A

WNV Development Cost—Gen-Probe

[***]

[***]

[***]

[***]

--------------------------------------------------------------------------------

Schedule 1.4B

WNV Development Cost—Chiron

[***]

[***]

--------------------------------------------------------------------------------

Schedule 1.17.

Description of WNV Assay Product

        The WNV Assay Product is an in vitro nucleic acid amplification test for
the qualitative detection of West Nile Virus in human plasma for use in the
Blood Screening Field. The WNV Assay Product is to be developed to run initially
on the Procleix semi-automated instrument (eSAS).

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Schedule 5

WNV Development Costs

        1.     Reimbursable FTE Rate. Budgets for future years will be based on
$[***] per FTE per calendar until the budget for the year in question is
finalized each year per Section 5.2.1(b). Until each years budget is agreed upon
[***] budget payments per Section 5.3.2 will be based upon the previous years
agreed rate per Section 5.2.1(b) subject to true-up once new rates have been
agreed.

        2.     WNV Development Costs included within FTE Labor Rate. WNV
Development Costs included within FTE Labor Rate consist of all attributable
costs associated with the development of the WNV Assay Product and modifications
to associated instrument system platforms (but excluding Tigris instruments)
that may be required for such WNV Assay Product (calculated in accordance with
United States generally accepted accounting principles, or as otherwise mutually
agreed in writing between the parties) incurred prior to the Completion Date and
includes pilot development; validation studies necessary for product and process
licensure; clinical studies; licensing activities; and the manufacture and
ultimate disposition of conformance lots of material, calculated as follows:

        (a)   Shared development costs include: research and development
associated with the WNV Development Program; clinical studies; validation
exclusively associated with the particular analyte; development lots; document
preparation specific to the development;

        (b)   The planned resources, and the associated costs, will be broken
out on a [***] basis and analyzed against the Resource Plan included within the
Technical Plan, and reflected in the Budget;

        (c)   Salaried staff costs included within the Budget will be adjusted
to reflect actual staff costs. Salary information may be aggregated to protect
the identity of individuals. This salary information will be verifiable on a
need to know basis to a select number of personnel from each company;

        (d)   Cost for wage laborers plus the applicable overhead charge for
such labor (calculated at the rates and charges described in Section 5.2.1) paid
to personnel described in the Resource Plan, including the WNV Development
Program project manager and personnel engaged to perform QA testing for the WNV
Development Program;

        (e)   Costs for engineering prototypes and manufacturing pilot modules
required for the WNV Development Program;

        (f)    Costs of inventory consumed in the WNV Development Program,
including raw material, intermediates and finished goods, and conformance lots,
whether reject or not, that arise from the WNV Development Program or are
necessary to support the WNV Development Program, and scrap material, including
raw materials and development materials that arise from the WNV Development
Program but excluding WNV Assay Product and scrap materials used strictly for
internal research purposes or consumed in development programs other than the
WNV Development Program;

        (g)   Costs for conformance product documentation;

        (h)   Costs for courier and mail service fees for delivery of items
between Gen-Probe and Chiron;

        (i)    Costs of travel, lodging and reasonable per diem expenses for
employee and consultants of Gen-Probe or Chiron incurred in furtherance of their
activities hereunder, providing training or participating on the Supervisory
Board to the extent such costs are not included within the overhead charge
applicable to labor costs;

        (j)    Costs of foreign registration, marketing studies to support
registration, and market research costs necessary to better define requirements
or to support national decision-making;

        (k)   Such other categories as the parties may agree from time to time
using the approval process described in Section 5.2.

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        (l)    All budgeted expenses of Departments directly involved with the
WNV Development Program

        (m)  Appropriate portions of budgeted costs of departments indirectly
involved in the WNV Development Program.

        3.     WNV Development Costs not included within FTE Labor Rate.

        (a)   Cost of conformance lot materials consumed in performance of WNV
Development Program or clinical trials.

        (b)   Significant Third Party consultant charges (i.e. CRO, regulatory
expertise, etc.) to the extent not captured within the FTE rates in Item 2
above.

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Schedule 5.2.3

WNV Development Costs Calculation Methodology

[***]

[***]

--------------------------------------------------------------------------------

Schedule 5.3.1

Accrued WNV Development Costs

[***]

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Schedule 5.3.2

[***] Budgeted Payments

        The party with the negative delta shall submit to the other party, on or
before the end of the [***] during the term of the WNV Development Program, an
invoice setting forth the amount of the delta. In addition, any party owed by
other an excess adjustment shall submit to the other party, on or before the end
of the [***] during the term of the WNV Development Program, an invoice setting
forth the amount of the excess adjustment, providing reasonable detail for any
WNV Development Costs not previously invoiced and requesting payment of [***] of
the total amount. WNV Development Costs by the invoicing party incurred to date
and not yet reimbursed as provided herein, providing reasonable detail for any
WNV Development Costs not previously invoiced and requesting payment of [***] of
the total amount. Each party shall pay on or before the date specified therefore
on the Technical Plan an amount equal to the lesser of (i) the WNV Development
Costs reflected on the invoice submitted to such party on account of such
payment (together with amounts reflected on earlier invoices not previously
reimbursed) or (ii) the amount of the payment described on the attached
Technical Plan. To the extent that a reimbursement payment is inadequate to
cover the total WNV Development Costs incurred to date by a party, then each
party shall carry over the balance to the next subsequent payment(s) until
finally reimbursed in full.

        By way of example, and using hypothetical dollars for actual
expenditures, the calculation would operate as follows:

[***]   [***]   [***]   [***]               [***]   [***]       [***] [***]  
[***]   [***]   [***]

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Schedule 5.3.3

[***] True-Up Payments
(sample methodology)

        By way of example, and using hypothetical dollars for actual
expenditures, the calculation would operate as follows: (true-up payment due to
Chiron in this case):

[***]   [***]   [***]   [***]   [***]   [***]   [***]                          
[***]   [***]       [***]   [***]   [***]   [***] [***]   [***]   [***]   [***]
  [***]       [***]

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QuickLinks

FUTURE BLOOD SCREENING ASSAY— WEST NILE VIRUS ADDENDUM AMENDING AGREEMENT
ENTERED INTO AS OF JUNE 11, 1998 BY AND BETWEEN GEN-PROBE INCORPORATED, A
DELAWARE CORPORATION AND CHIRON CORPORATION
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