<PAGE>

                                                                   EXHIBIT 10.14

                                            ***TEXT OMITTED AND FILED SEPARATELY
                                                CONFIDENTIAL TREATMENT REQUESTED
                                           UNDER 17 C.F.R. Sections 200.80(b)(4)
                                                                   AND 240.24B-2

                          FUTURE BLOOD SCREENING ASSAY-

                                 ULTRIO ADDENDUM

                                    AMENDING

                   AGREEMENT ENTERED INTO AS OF JUNE 11, 1998

                                 BY AND BETWEEN

                 GEN-PROBE INCORPORATED, A DELAWARE CORPORATION

                                       AND

                               CHIRON CORPORATION

<PAGE>

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                                    Page
                                                                                                                    ----
<S>                                                                                                                 <C>
1.       Definitions.............................................................................................      1

         1.1      Agreement......................................................................................      1

         1.2      Binder.........................................................................................      1

         1.3      Budget.........................................................................................      1

         1.4      Completion Date................................................................................      1

         1.5      FTE Labor Rate.................................................................................      1

         1.6      Interim Events.................................................................................      1

         1.7      Material Modification..........................................................................      1

         1.8      NIH Monies.....................................................................................      1

         1.9      Non-material Modification......................................................................      2

         1.10     Product Requirements Document..................................................................      2

         1.11     Project Management.............................................................................      2

         1.12     Resource Plan..................................................................................      2

         1.13     Software Requirements Specifications...........................................................      2

         1.14     Technical Plan.................................................................................      2

         1.15     Timeline.......................................................................................      2

         1.16     Ultrio Assay Product...........................................................................      2

         1.17     Ultrio Development Costs.......................................................................      2

         1.18     Ultrio Development Program.....................................................................      2

2.       Ultrio Development Program..............................................................................      3

         2.1      Objective......................................................................................      3

         2.2      General Conduct of Development.................................................................      3

         2.3      No Guarantee...................................................................................      3

         2.4      Project Management.............................................................................      3

                  2.4.1    Principles of Project Management......................................................      3
</TABLE>

                                       i.

<PAGE>

                                TABLE OF CONTENTS
                                   (Continued)

<TABLE>
<CAPTION>
                                                                                                                     Page
                                                                                                                     ----
<S>                                                                                                                  <C>
                  2.4.2    Project Manager.......................................................................      4

                  2.4.3    Project Manager's Responsibilities....................................................      4

                  2.4.4    Project Leaders.......................................................................      5

                  2.4.5    Reports...............................................................................      5

                  2.4.6    Meetings of the Supervisory Board.....................................................      5

         2.5      Development Responsibilities...................................................................      5

                  2.5.1    Principal Responsibility; General Statement...........................................      5

                  2.5.2    Shared Responsibility.................................................................      6

                  2.5.3    Principal and Shared Responsibility; Specific Allocation..............................      6

                  2.5.4    Regulatory/Licensure..................................................................      7

                  2.5.5    Project Leader Disagreements..........................................................      7

3.       Modifications...........................................................................................      7

         3.1      Ultrio Development Program Definition..........................................................      7

         3.2      Modifications..................................................................................      7

                  3.2.1    Request for Modifications.............................................................      7

                  3.2.2    Non-Material Modifications............................................................      8

         3.3      Material Modifications.........................................................................      8

                  3.3.1    Request for Material Modifications....................................................      8

                  3.3.2    Initial Analysis of Impact of Proposed Material Modification..........................      8

                  3.3.3    Preparation of Modified Ultrio Development Program....................................      8

                  3.3.4    Acceptance of Modified Ultrio Development Program.....................................      9

                  3.3.5    Effective Date of Modified Ultrio Development Program.................................      9

         3.4      Notice of Significant Changes..................................................................     10

4.       Changes to Ultrio Assay Product after Completion Date...................................................     10

         4.1      Process........................................................................................     10

         4.2      Additional Work under Addendum.................................................................     10
</TABLE>

                                       ii.

<PAGE>

                                TABLE OF CONTENTS
                                   (Continued)

<TABLE>
<CAPTION>
                                                                                                                    Page
                                                                                                                    ----
<S>                                                                                                                 <C>
5.       Ultrio Development Costs................................................................................    10

         5.1      [...***...]Ultrio Development Costs and [...***...]............................................    10

         5.2      Definition and Calculation of Ultrio Development Costs; [...***...]............................    11

                  5.2.1    Ultrio Development Costs; FTE Labor Rate..............................................    11

                  5.2.2    Comparison with Resource Plan.........................................................    12

                  5.2.3    Methodology...........................................................................    12

         5.3      Payment of Ultrio Development Costs............................................................    12

                  5.3.1    Accrued Ultrio Development Costs......................................................    12

                  5.3.2    [...***...] Budgeted Payments.........................................................    13

                  5.3.3    [...***...] True-Up Payments..........................................................    13

                  5.3.4    Invoices..............................................................................    13

         5.4      Dispute........................................................................................    13

         5.5      Right to Audit and Verify......................................................................    13

6.       Manufacturing and Commercialization.....................................................................    14

         6.1      Definitions Relevant to Manufacturing and Commercialization Obligation.........................    14

                  6.1.1    Applicable Purchase Price.............................................................    14

                  6.1.2    Transfer Price........................................................................    14

                  6.1.3    Manufacturing Cost....................................................................    14

                  6.1.4    Rare Reagents.........................................................................    14

         6.2      Right to Audit and Verify......................................................................    14

         6.3      Non-Commercial Products........................................................................    14

         6.4      Commercialization Budget.......................................................................    15

7.       License Grants..........................................................................................    16

8.       Addendum Effective Date; Term; Termination..............................................................    16

         8.1      Term of Ultrio Addendum........................................................................    16

         8.2      Termination for Breach.........................................................................    16
</TABLE>

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      iii.

<PAGE>

                                TABLE OF CONTENTS
                                   (Continued)

<TABLE>
<CAPTION>
                                                                                                                   Page
                                                                                                                   ----
<S>                                                                                                                <C>
                  8.2.1    Default...............................................................................    16

                  8.2.2    Right to Cure Event of Default........................................................    17

                  8.2.3    Effect of Termination for Breach......................................................    17

         8.3      Termination by Both Parties....................................................................    17

                  8.3.1    Vote to Terminate.....................................................................    17

                  8.3.2    Effect of Notice Period on Termination by Both Parties................................    17

                  8.3.3    Effect of Termination by Both Parties.................................................    18

         8.4      Termination by Either Party; Unilateral Withdrawal from Ultrio Development Program.............    18

         8.5      Continuance of Ultrio Development Program following Unilateral Withdrawal or Termination.......    18

                  8.5.1    Election..............................................................................    18

                  8.5.2    Funding and Conduct of Development....................................................    18

                  8.5.3    Reimbursement of Development Costs....................................................    19

                  8.5.4    Control of the Program upon Unilateral Funding........................................    20

                  8.5.5    Rights under Agreement................................................................    20

9.       Escalation..............................................................................................    21

         9.1      Escalation Process.............................................................................    21

         9.2      Remedies in Event of Default...................................................................    21

         9.3      Survival.......................................................................................    21

10.      No Other Amendment......................................................................................    21

11.       Counterparts...........................................................................................    22
</TABLE>

                                       iv.

<PAGE>

                          Future Blood Screening Assay-

                                 ULTRIO ADDENDUM

         This Future Blood Screening Assay - Ultrio Addendum (the "Ultrio
Addendum") is entered into, effective as of January 1, 2001 (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), (vii) 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 the proposed development of a
triplex TMA assay for the detection of human immunodeficiency virus (HIV),
hepatitis C virus (HCV), and/or hepatitis B virus (HBV), 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 (the "Ultrio
Assay").

         D.       Gen-Probe applied for and received a contract with the
National Institutes of Health, Contract N01-HB-07148, effective January 1, 2000,
for which Chiron submitted a supporting letter, which contract as amended
provides for, among other things, the partial funding of costs associated with
the development of the Ultrio Assay.

         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. These
settlement agreements addressed certain aspects of the development of the Ultrio
Assay, the funding of such development, and eventual sale of any developed
Ultrio Assay. All provisions of these settlement agreements which address the
subject matter addressed in this Addendum are expressly superceded by this
Ultrio Addendum, except as expressly described herein.

         F.       By this Ultrio Addendum, the parties desire to include the
Ultrio 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 Ultrio Addendum.

<PAGE>

                                    Agreement

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

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

         1.1 Agreement shall mean the June 11, 1998 Collaboration Agreement, as
amended in the manner described in Recital A.

         1.2 Binder means that certain three-ring binder, with one or more
volumes, entitled "Ultrio Development Program for the Ultrio Assay Product
(Gen-Probe/Chiron Ultrio Development Addendum, dated as of January 1, 2001)
Binder," in which certain documents, materials or other items incorporated into
this Ultrio Addendum by reference are kept. The original Binder and an
additional volume of the Binder, labeled "Amendments to Ultrio 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.

         1.3 Budget means the budgeted Ultrio Development Costs of the Ultrio
Development Program. The Budget shall include the estimated cost of the Ultrio
Development Program on a monthly basis through the end of the Ultrio 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.

         1.4 Completion Date means a date which is [...***...].

         1.5 FTE Labor Rate is defined in Section 5.2.1.

         1.6 Interim Events means such events of material significance to the
Ultrio 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 Ultrio
Addendum.

         1.7 Material Modification means a change or amendment to the Ultrio
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.

         1.8 NIH Monies means all monies actually paid to Gen-Probe by the NIH
specifically to defray Ultrio Development Costs under (i) the NIH contract
referenced in Recital D above (ii) any extensions or amendments to the NIH
contract referenced in Recital D, and (iii) any other contract or grant under
which Gen-Probe seeks reimbursement for Ultrio 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 Ultrio
Development Costs. so long as Gen-Probe can reasonably demonstrate that monies
paid do not relate to the Ultrio Development Program.

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                        1.

<PAGE>

         1.9 Non-material Modification means a change or amendment to the Ultrio
Development Program other than a Material Modification. Written agreement among
members of Project Management that a modification is a "Non-material
Modification" hereunder as described in Section 3.2 below shall be conclusive.

         1.10 Product Requirements Document (or "PRD") means the specifications
for the Ultrio 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 A, dated May 16, 2001)," and may be amended from time to time under the
provisions of Section 3 below.

         1.11 Project Management is defined in Section 2.4.1.

         1.12 Resource Plan means the description of (i) a party's personnel to
be allocated to the Ultrio 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 Ultrio 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 Ultrio
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.

         1.13 Software Requirements Specifications (or "SRS") means the
specifications for the software component of the Ultrio Development Program. The
initial Software Requirements Specifications are described in the Binder, under
the heading "Software Requirements Specifications (SRS, Revision C, dated
October 1 , 2002)," and may be amended from time to time under the provisions of
Section 3 below.

         1.14 Technical Plan means the statement of work prepared for the
development of the Ultrio 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 A, dated June 27, 2001," and
may be amended from time to time under the provisions of Section 3 below.

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

         1.16 Ultrio Assay Product is defined on Schedule 1.16 and expressly
excludes any products or instruments in the Clinical Diagnostic Field.

         1.17 Ultrio Development Costs means, with respect to this Ultrio
Addendum only, the development costs defined in Section 5 hereof.

         1.18 Ultrio Development Program means the statement of work for the
development of the Ultrio Assay Product under the terms of this Ultrio 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.

                                       2.
<PAGE>

2. Ultrio Development Program.

         2.1 Objective. Subject to the terms of the Agreement, as amended by
this Ultrio Addendum, the parties each shall conduct their respective
obligations under the Ultrio Development Program as established in accordance
with the terms hereof, and shall conduct such clinical trials and apply for and
endeavor to obtain such regulatory approvals as necessary or appropriate to make
and sell the Ultrio Assay Product in the Territory for use in the Blood
Screening Field.

         2.2 General Conduct of Development. The parties shall conduct their
respective obligations under the Ultrio 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 Ultrio Development Program and shall use their respective
Commercially Reasonable Efforts to achieve the objectives of the Ultrio
Development Program efficiently and expeditiously. The parties each shall
allocate such personnel, equipment, facilities and other resources to the Ultrio
Development Program to carry out their respective obligations and to accomplish
the objectives thereof, all as is more particularly described in the Ultrio
Development Program, as amended from time to time during the term of this Ultrio
Addendum (in accordance with the provisions of Section 3). Each party shall have
the right to consult with the other party regarding the Ultrio 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 Ultrio Development
Program (as amended from time to time during the term of this Ultrio 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 Ultrio 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 Ultrio Assay Product, even though
each party exercises Commercially Reasonable Efforts and commits the resources
described in the Ultrio 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 Ultrio Development Program, even if
such resources fail to successfully complete the development of the Ultrio Assay
Product, or to complete the development of the Ultrio 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 Ultrio
Development Costs between the parties shall be due and payable without respect
to the achievement of any particular deliverable specified in the Ultrio
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 Ultrio 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 Ultrio 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

                                       3.
<PAGE>

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 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 Ultrio 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 Ultrio Development Program,
with the Project Manager. The primary point of contact for the Ultrio
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 Ultrio 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 Ultrio Assay Product will be managed under a Project Manager, the
responsibilities of which are described in Section 2.4.3. The Ultrio 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 Ultrio
Development Program under this Ultrio 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 Ultrio 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

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                       4.
<PAGE>

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 Ultrio Addendum;

                           (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 Ultrio 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 Ultrio 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 Ultrio
Development Program, has allocated sufficient personnel, equipment, facilities
and other resources to achieve the objectives of the Ultrio 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 Ultrio 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 Ultrio 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 Ultrio Development Program to assess progress of the
development and the potential for commercialization of the Ultrio 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

                                       5.
<PAGE>

approval process more particularly described in Section 3 below shall be
governed. The parties intend that portions of the Ultrio 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 Ultrio Development
Program. The parties' obligations with respect to certain warehousing and
shipping are subject to Amendment No. 3.

                  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 Ultrio 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 Ultrio
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:

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------------------
Function                            Principal Responsibility                    Shared Responsibility
<S>                                 <C>                                         <C>
-----------------------------------------------------------------------------------------------------
[...***...]                               Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                               Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                               Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe*
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe*
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe*
-----------------------------------------------------------------------------------------------------
[...***...]                                                                     Gen-Probe/Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                                                                     Gen-Probe/Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                               Gen-Probe
-----------------------------------------------------------------------------------------------------
[...***...]                                                                     Gen-Probe/Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                               Chiron
-----------------------------------------------------------------------------------------------------
[...***...]                                                                     Gen-Probe/Chiron
-----------------------------------------------------------------------------------------------------
</TABLE>

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                       6.
<PAGE>

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------
Function                                     Principal Responsibility            Shared Responsibility
<S>                                          <C>                                 <C>
------------------------------------------------------------------------------------------------------
[...***...]                                       Gen-Probe
------------------------------------------------------------------------------------------------------
[...***...]                                       Gen-Probe
------------------------------------------------------------------------------------------------------
[...***...]                                       Gen-Probe
------------------------------------------------------------------------------------------------------
[...***...]                                       Gen-Probe
------------------------------------------------------------------------------------------------------
[...***...]                                       Chiron
------------------------------------------------------------------------------------------------------
[...***...]                                       Chiron
------------------------------------------------------------------------------------------------------
[...***...]                                                                      Gen-Probe/Chiron
------------------------------------------------------------------------------------------------------
</TABLE>

         *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 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 Ultrio Development Program Definition. The parties have prepared
and agreed upon a Ultrio Development Program, as described in the Binder. The
Ultrio 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 Ultrio 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 Ultrio Addendum establish a process by which the parties will amend
the Ultrio 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 Ultrio
Development Program from time to time during the term of this Ultrio 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

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                       7.
<PAGE>

described in this Section 3. Changes, modifications or improvements to the
Ultrio 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 Ultrio 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
modification which (i) reflects an increase in the actual Ultrio Development
Costs incurred that, when aggregated with all previously authorized
modifications, of greater than [...***...] over the Development Costs reflected
in the original Budget approved in effect as of the date this Ultrio Addendum
was executed by the parties, or (ii) contains a proposal to alter any Interim
Event as compared to the most recently approved Timeline shall be deemed to be a
Material Modification. 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.

         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 Ultrio 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 Ultrio 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
Ultrio Assay Product. Should either party conclude, in its reasonable
discretion, that the potential for [...***...] by any proposed change to the
Ultrio Development Program requested in accordance with this Section 3.3, such
party may elect to terminate participation in the Ultrio Development Program
under the provisions of Section 8.4.

                  3.3.3 Preparation of Modified Ultrio Development Program.
Unless the parties terminate the Ultrio Development Program for convenience
under Section 8.3 below or a party terminates on unilateral withdrawal under
Section 8.4 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

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                       8.
<PAGE>

below. Costs incurred by Gen-Probe and Chiron to prepare such response to the
request shall be included in Ultrio Development Costs hereunder.

                  3.3.4 Acceptance of Modified Ultrio Development Program.

                           (a) Unless the parties terminate the Ultrio
Development Program for convenience under Section 8.3 below or a party
terminates on unilateral withdrawal under Section 8.4 below, the parties shall
promptly, but not later than [...***...] after preparation by the parties of a
modified Ultrio Development Program under Section 3.3.3 meet and consult with
respect to the proposed modified Ultrio Development Program. Either party may
elect to terminate participation in the Ultrio Development Program under the
provisions of Section 8.4 below if the requested modification is a Material
Modification, determined in accordance with Section 3.2.1. If neither party
terminates under Sections 8.3 or 8.4 below, then neither party may unreasonably
withhold approval of any request for modification of the Ultrio Development
Program.

                           (b) If neither party terminates under Sections 8.3 or
8.4 below, then the parties shall thereafter finalize such modified Ultrio
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 Ultrio
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 Ultrio Development
Program to reflect the discussions of the parties, and redeliver the revised
proposed modified Ultrio 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 Ultrio
Development Program, or (ii) [...***...], meet and discuss the proposed Material
Modification to Ultrio 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 Ultrio 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 Ultrio 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 Ultrio Development Program.
At such time as the parties (or, if applicable, the Supervisory Board) shall
have accepted a modified Ultrio 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
Ultrio Development Program as so modified and approved shall constitute the
Ultrio Development Program hereunder and be

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                       9.
<PAGE>

incorporated by reference into this Ultrio Addendum, and shall supersede the
preceding Ultrio Development Program, or applicable portions thereof, for all
purposes. In order to evidence their agreement to the revised Ultrio Development
Program, the parties shall include it in an additional volume of the Binder,
labeled "Amendments to Ultrio Development Program," in which all amendments and
modifications to the Ultrio 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 Ultrio 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 Ultrio 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 Ultrio 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 Ultrio Assay Product. The
Supervisory Board shall promptly, but not later than the latter of (i)
[...***...] a party of such request for such changes to the Ultrio 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 can be implemented
under the terms of this Ultrio 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
Ultrio Addendum, then the parties shall implement the process more particularly
described in Section 3.3 above, and the Supervisory Board may approve a new
Ultrio 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 Ultrio Assay Product, without
regard to whether the other party indicates a willingness to pay some portion or
the entire costs of such development.

5. Ultrio Development Costs.

         5.1 [...***...] Ultrio Development Costs and [...***...]. Each party is
responsible for and agrees to pay [...***...], as defined in and subject to
Section 5.2 below, [...***...]. Such costs shall be payable as described in
Section 5.3 herein. The Budget has been prepared for the purpose of permitting
the parties to plan for Ultrio Development Program expenditures related to
Ultrio Development Costs hereunder and represents the parties' best estimate of
such Ultrio Development Costs, but does not represent a "fixed price maximum" or
other guaranteed maximum cost of the development required for the Ultrio
Development Program.

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      10.
<PAGE>

         5.2 Definition and Calculation of Ultrio Development Costs;
[...***...]. "Ultrio Development Cost" with respect to the Ultrio Development
Program means the fully-burdened cost of conducting the research and development
(including clinical trials and domestic and international regulatory
submissions) of the Ultrio Assay Product, and shall include (i) [...***...], and
(ii) [...***...]. "Ultrio Development Costs" shall not include [...***...].
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 Ultrio Development Costs; FTE Labor Rate.

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

                           (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
Ultrio Addendum.

                           (d) In addition to the foregoing, throughout the term
of this Ultrio 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

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      11.
<PAGE>

                                    (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 "Ultrio Development Costs
Calculation Methodology".

                           (e) In the event aggregate actual Ultrio 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). [...***...] of each year 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 "Ultrio 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 Ultrio Development
Costs included within the FTE Labor Rate and the reimbursed Ultrio 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 difference
between the actual Ultrio Development Costs included within the FTE Labor Rate
and the reimbursed Ultrio Development Costs included within the FTE Labor Rate.

                           (f) Ultrio 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 Ultrio 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 Ultrio Development Costs. In addition to the provisions
of Article 7 of the Agreement, the parties agree as follows:

                  5.3.1 Accrued Ultrio Development Costs. Each party has already
incurred, prior to the date of execution of this Ultrio Addendum, certain Ultrio
Development Costs. To the extent that one party has paid more than its
[...***...] share of the aggregate Ultrio Development Costs incurred prior to
and until the date of execution of this Ultrio Addendum, [...***...], the other
party will reimburse such party for [...***...] the Ultrio Development Costs
paid by that

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      12.
<PAGE>

party and [...***...] of the aggregate Ultrio Development Costs incurred prior
to and until the date of execution of this Ultrio Addendum. Attached to this
Ultrio Addendum as Schedule 5.3.1 is a summary of the Ultrio Development Costs
incurred by the parties prior to the execution of this Ultrio Addendum, which
includes an itemized summary of the NIH Monies received prior to the execution
of this Ultrio Addendum.

                  5.3.2 [...***...] Budgeted Payments. Each party's respective
[...***...] share of Ultrio Development Costs (after [...***...]) will be paid
on a [...***...] in an amount equal to the amount reflected in Budget for that
[...***...]. The Budget sets forth the parties' anticipated expenditures and FTE
Labor amounts for Ultrio Development Costs [...***...] during the term of the
Ultrio 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 Ultrio
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 Ultrio 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 party will calculate the actual FTE Labor hours expended on the Ultrio
development Program during [...***...]. 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 Ultrio Development Costs not included in the FTE Labor
hours during the [...***...], 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.

                  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 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 Ultrio Development
Program by reason of such dispute.

         5.5 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 Ultrio Development Costs hereunder, in accordance with the
provisions of

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      13.
<PAGE>

Section 7.3 of the Agreement, including without limitation actual expenditures
and amounts received as NIH Monies after the Addendum Effective Date but prior
to the execution of this Ultrio Addendum.

6. Manufacturing and Commercialization.

         6.1 Definitions Relevant to Manufacturing and Commercialization
Obligation. The parties intend that the Ultrio 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 Ultrio Assay Product is as set
forth in Section 1.2.1 of the Agreement. The parties acknowledge that the Ultrio
Assay Product is a Future Blood Screening Assay which includes as a constituent
element an assay for HCV (other than those sold pursuant to Sections 3.1.4(b) or
3.6 of the Agreement), for which the provisions of Section 1.2.1 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 Ultrio Assay Product in the
Territory will never be less than [...***...].

                  6.1.2 Transfer Price. The "Transfer Price" applicable to the
Ultrio Assay Product is set forth in Section 1.58.2 of the Agreement except that
the Transfer Price for Ultrio 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 Ultrio Development Costs. The Transfer Price will never be less than the
Manufacturing Cost for the Ultrio Assay Product. 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, shall never be less than
the [...***...]."

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

                  6.1.4 Rare Reagents. The Ultrio 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 Ultrio Assay Product manufactured for the Ultrio
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 Ultrio Development Program, including without limitation research
studies or marketing studies performed in support of commercialization of the
Ultrio Assay Product, or the development and clinical trials for the Tigris
instrument, the party selling or utilizing such Ultrio Assay Product shall
reimburse the Ultrio Development Program to the extent that the program was
charged for the materials.

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      14.
<PAGE>

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

         "(b) Gen-Probe agrees to provide to Chiron reasonable quantities of the
         Ultrio 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
         Ultrio Assay Products"). The entire compensation to 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 Ultrio Assay
         Products ordered by Chiron as well as quantities of Ultrio Assay
         Products consumed by Gen-Probe for all purposes other than the Ultrio
         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 Ultrio Addendum for breach in
accordance with Section 8.2 or an unilateral withdrawal by a party in accordance
with Section 8.4, and the timely election by a Continuing Party to continue the
Ultrio 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 Ultrio 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 Ultrio 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) [...***...], meet and discuss the proposed
commercialization budget.

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      15.
<PAGE>

                           (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 Ultrio Development
Program shall be governed by Sections 3.2.6 and Section 9 of the Agreement.
Chiron agrees that Gen-Probe shall be [...***...].

8. Addendum Effective Date; Term; Termination.

         8.1 Term of Ultrio Addendum. This Ultrio 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 purpose of the Ultrio Assay Product, the "Blood
Screening Term" shall mean the period commencing on the Addendum Effective Date
and expiring on [...***...] after the First Commercial Sale of the Ultrio Assay
Product. Termination of this Ultrio Addendum shall be governed by the terms of
this Section 8 and termination of the Agreement is governed by Section 11.2 of
the Agreement.

         8.2 Termination for Breach.

                  8.2.1 Default. Either party (the "nondefaulting party") has
the right, upon written notice to the other party (the "defaulting party"), to
terminate the Ultrio 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 Ultrio 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 Ultrio Development
Program or to exercise Commercially Reasonable Efforts achieve the objectives of
the Ultrio Development Program; provided, however, that the failure to
successfully complete the development of the Ultrio Assay Product, or to
complete the development of the Ultrio 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 Ultrio Addendum; and

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

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      16.
<PAGE>

                  8.2.2 Right to Cure Event of Default. Upon the occurrence of
any event of default entitling a party to terminate this Ultrio 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 Ultrio
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".)

                  8.2.3 Effect of Termination for Breach. Upon a termination of
this Ultrio Addendum for default under this Section 8.2:

                           (a) Subject to the rights of the parties under
Section 9.3, the Ultrio 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 Ultrio Assay Product, shall remain
in full force and effect unchanged.

                           (d) The defaulting party's rights under the Agreement
with respect to the Ultrio Assay Product shall terminate and be of no further
force and effect. The defaulting party may not undertake a development
substantially similar to the Ultrio 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) [...***...], and (iii)
[...***...].

         8.3 Termination by Both Parties.

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

                  8.3.2 Effect of Notice Period on Termination by Both Parties.
During the notice period as set forth in Section 8.3.1, 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 Ultrio 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 8.2 or the
effective date of withdrawal under Section 8.4 of the Ultrio Development
Program), each party shall pay, promptly upon receipt of an invoice therefor, to
the other

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      17.
<PAGE>

party an amount equal to (i) all Ultrio Development Costs accrued to date in the
terminated Ultrio Development Program for which an invoice has been rendered and
(ii) all Ultrio Development Costs not yet invoiced but incurred in the
terminated Ultrio Development Program, whether or not disputed, as set forth in
the approved Budget.

                  8.3.3 Effect of Termination by Both Parties. Upon any
termination of the Ultrio Development Program under this Section 8.3, 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.

         8.4 Termination by Either Party; Unilateral Withdrawal from Ultrio
Development Program. Either party (referred to for convenience as the
"withdrawing party") may elect to terminate this Ultrio Addendum under this
Section 8.4 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
Ultrio Development Program requested in accordance with Section 3.3 above; or

                           (b) The withdrawing party receives a request for a
Material Modification of the Ultrio 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 Ultrio Addendum under this Section 8.4
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 Ultrio
Addendum. (The notice of intent to withdraw described in this Section 8.4 is
referred to for convenience as the "withdrawal notice"; and a date which is
[...***...] is referred to for convenience as the "effective date of
withdrawal").

         8.5 Continuance of Ultrio Development Program following Unilateral
Withdrawal or Termination.

                  8.5.1 Election. Following any termination of this Ultrio
Addendum for breach in accordance with Section 8.2 or an unilateral withdrawal
by a party in accordance with Section 8.4, the non-defaulting party (under
Section 8.2) or the non-withdrawing party (under Section 8.4) (referred to for
convenience as the "Continuing Party") may elect to continue the Ultrio
Development Program by providing written notice to the other party on or before
the effective date of termination under Section 8.2 or the effective date of
withdrawal under Section 8.4.

                  8.5.2 Funding and Conduct of Development.

                           (a) If a Continuing Party elects pursuant to this
Section 8.5 to continue funding the Ultrio Development Program, such Continuing
Party shall be solely responsible for the current funding of all Ultrio
Development Costs from and after the effective date of termination under Section
8.2 or the effective date of withdrawal under Section 8.4, subject to the right
to reimbursement more particularly described below.

                           (b) In addition to Section 8.5.2(a), if the
Continuing Party is Chiron, Chiron shall pay Gen-Probe [...***...]

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      18.
<PAGE>

[...***...]. Such amount shall be payable in accordance with the provisions of
Section 5.3, including without limitation monthly payment against Budget and
monthly true-up payments. Chiron shall be entitled to reimbursement of such
amounts paid in accordance with the provisions of Section 8.5.3 below. In the
event, however, that Chiron shall elect to cease the development, marketing and
sale of the Ultrio Assay Product prior to the effective commercialization
thereof, then Chiron shall pay Gen-Probe an additional amount equal to
[...***...] of the total aggregate Ultrio Development Costs (meeting the
definition and calculated as described in Section 5.2) incurred by Gen-Probe
from and after the effective date of termination for breach under Section 8.2 or
the date of receipt from Gen-Probe of the withdrawal notice delivered pursuant
to Section 8.4 of the Ultrio Addendum, which additional amount the parties agree
will compensate Gen-Probe for the resources committed by Gen-Probe to the Ultrio
Development Program which did not result in an effectively commercialized Ultrio
Assay Product. Chiron shall pay such additional amount promptly upon ceasing
such development, as permitted under Section 3.2.1(c) of the Agreement.

                           (c) In addition to Section 8.5.2(a), if the
Continuing Party is Gen-Probe, in the event that Gen-Probe shall elect to cease
the development, marketing and sale of the Ultrio Assay Product prior to the
effective commercialization thereof, then Gen-Probe shall pay Chiron an
additional amount equal to [...***...] of the total aggregate commercialization
costs incurred by Chiron as approved in the commercialization budget under
Section 6.4 to be incurred prior to the effective commercialization of the
Ultrio Assay Product. Gen-Probe shall pay such additional amount promptly upon
ceasing such development, as permitted under Section 3.2.1(c) of the Agreement.

                  8.5.3 Reimbursement of Development Costs. The party electing
to continue development under the terms of Section 8.5 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 8.2 or the effective date of withdrawal under Section 8.4 of the
Ultrio Development Program as a joint development program under this Ultrio
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 8.5 of the Ultrio 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 8.2 or the effective date of withdrawal under Section
         8.4, as the case may be (the "Post-Withdrawal Development Costs"), as
         follows:

                  i. If the funding party is Gen-Probe, Chiron shall (A)
         [...***...]; (B) [...***...]; (C) [...***...]

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      19.
<PAGE>

         [...***...]; (D) [...***...]; (E) [...***...]; and (F) [...***...].
         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 (A) [...***...]; (B)
         [...***...]; (C) [...***...]; (D) [...***...]; and (E) [...***...].
         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 Ultrio Assay
         Product revenues pursuant to Section 3.2.1(b)(i) above or Section
         3.2.1(b)(ii) above, as applicable."

                  8.5.4 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 8.2 or the effective date
of withdrawal under Section 8.4. The Continuing Party shall have the right to
make such Material Modifications to the Ultrio 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 Ultrio Addendum.
Notwithstanding the above, the Continuing Party shall remain obligated to
provide the other party with a copy of the Ultrio Development Program, and all
notice and reporting obligations set forth herein shall remain in full force and
effect.

                  8.5.5 Rights under Agreement. Except as expressly modified by
this Section 8.5, the parties shall retain all rights and obligations allocated
pursuant to Section 3.2 of the Agreement. Without

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      20.
<PAGE>

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 Ultrio Assay Product; Chiron shall have
the exclusive right to promote, market and sell the Ultrio 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 Ultrio 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 Ultrio Addendum, the following
provisions of this Ultrio Addendum shall survive such termination: Sections 2.3,
2.4.1, 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 Ultrio 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 Ultrio Addendum
and the Agreement, the terms of this Ultrio Addendum shall control. The
provisions of this Ultrio 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.

                                      21.
<PAGE>

11. Counterparts. This Ultrio 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.

         IN WITNESS WHEREOF, the parties have caused this Ultrio 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,                       CHIRON CORPORATION,
a Delaware corporation                        a Delaware corporation

By: /s/ Henry L. Nordhoff                     By: /s/ Jack Goldstein
--------------------------------------        ----------------------------------
Its: Chief Executive Officer                  Its: President, Blood Testing
Date: March 24, 2003                          Date: February 28, 2003

                                      22.
<PAGE>

                                 Schedule 1.16.

                       Description of Ultrio Assay Product

The Ultrio triplex assay is an in -vitro nucleic acid amplification test for the
qualitative detection of human immunodeficiency virus Type 1 ( HIV-1) RNA,
hepatitis B virus ( HBV) DNA, and/or hepatitis C virus( HCV) RNA in human plasma
for use in the Blood Screening Field. The Ultrio triplex assay will not
discriminate between HIV-1, HBV and HCV infection. The Ultrio assay is to be
developed to run initially on the Procleix semi-automated instrument (eSAS).

HIV-1, HBV and HCV discriminatory Probe reagents are in -vitro nucleic acid
amplification tests for the qualitative detection of the specified virus and are
provided with the Ultrio triplex assay as part of the Ultrio Assay Product for
use in discriminating between HIV-1, HBV and HCV in plasma following a positive
result from the Ultrio triplex assay.

For purposes of the foregoing Addendum, all of the Ultrio triplex assay and the
associated discriminatory probe reagents are included within the definition of
the "Ultrio Assay Product."

<PAGE>

                                   Schedule 5
                            Ultrio Development Costs

1. Reimbursable FTE Rate. Budget rates for future years will be based on
[...***...] per FTE per calendar year until finalized each year per section
5.2.1. Future calendar year FTE billing rates will be agreed to based on future
annual budgets. In the absence of agreement, the FTE billing rate will be the
then current billing rate subject to true-up once new rates have been agreed.

2. Ultrio Development Costs included within FTE Labor Rate. Ultrio Development
Costs included within FTE Labor Rate consist of all attributable costs
associated with the development of the Ultrio Assay Product and modifications to
associated instrument system platforms (but excluding Tigris instruments) that
may be required for such Ultrio 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 Ultrio 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
Ultrio Development Program project manager and personnel engaged to perform QA
testing for the Ultrio Development Program;

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

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

                           (g) Costs for conformance product documentation;

                                               *CONFIDENTIAL TREATMENT REQUESTED

                                      S5-1.

<PAGE>

                           (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 0.

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

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

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

                           (a) Cost of conformance lot materials consumed in
performance of Ultrio 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.

                                      S5-2.

<PAGE>

                                 Schedule 5.2.3

                Ultrio Development Costs Calculation Methodology

<PAGE>


                                 Schedule 5.3.1

                        Accrued Ultrio Development Costs

                                   [...***...]

                                               *CONFIDENTIAL TREATMENT REQUESTED

<PAGE>


                                 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 Ultrio 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 Ultrio Development
Program, AN invoice setting forth the amount of the excess adjustment, providing
reasonable detail for any Ultrio Development Costs not previously invoiced and
requesting payment of [...***...] of the total amount. Ultrio Development Costs
by the invoicing party incurred to date and not yet reimbursed as provided
herein, providing reasonable detail for any Ultrio 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 Ultrio 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 Ultrio 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:

<TABLE>
<S>               <C>             <C>            <C>
------------------------------------------------------------
[...***...]       [...***...]     [...***...]    [...***...]
------------------------------------------------------------

------------------------------------------------------------
[...***...]       [...***...]                    [...***...]
------------------------------------------------------------
[...***...]       [...***...]     [...***...]    [...***...]
------------------------------------------------------------
</TABLE>

                                               *CONFIDENTIAL TREATMENT REQUESTED

<PAGE>

                                 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):

<TABLE>
<S>                 <C>                 <C>                  <C>                  <C>               <C>              <C>
--------------------------------------------------------------------------------------------------------------------------------
[...***...]         [...***...]         [...***...]          [...***...]          [...***...]       [...***...]      [...***...]
--------------------------------------------------------------------------------------------------------------------------------

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

[...***...]         [...***...]                              [...***...]          [...***...]       [...***...]      [...***...]
--------------------------------------------------------------------------------------------------------------------------------

[...***...]         [...***...]         [...***...]          [...***...]          [...***...]                        [...***...]
--------------------------------------------------------------------------------------------------------------------------------
</TABLE>

                                               *CONFIDENTIAL TREATMENT REQUESTED