Exhibit 10.1


QUIDEL
CORPORATION


THIRD
AMENDMENT TO CREDIT AGREEMENT


This
THIRD AMENDMENT TO CREDIT AGREEMENT
(this “Amendment”) is dated as of April 5,
2007 and entered into by and among QUIDEL CORPORATION, a Delaware corporation
(“Borrower”), the financial institutions
listed on the signature pages hereof (“Lenders”), and BANK OF AMERICA, N.A., a
national banking association, as agent for Lenders (in such capacity,  “Agent”), and, for purposes of Section 5
hereof, each of the Guarantors listed on the signature pages hereof (“Guarantors”), and is made with reference to that certain
Credit Agreement dated as of January 31, 2005, as amended to the date hereof by
that certain Limited Waiver of Credit Agreement dated as of May 10, 2005, as
further amended by that certain First Amendment to Credit Agreement dated as of
June 24, 2005, and as further amended by that certain Second Amendment to
Credit Agreement dated as of September 1, 2005 (as so amended, the “Credit
Agreement”), by and
among Borrower, Lenders and Agent. 
Capitalized terms used herein without definition shall have the same
meanings herein as set forth in the Credit Agreement.


RECITALS


WHEREAS, Borrower and Lenders
desire to amend the Credit Agreement as set forth below;


NOW, THEREFORE, in
consideration of the premises and the agreements, provisions and covenants
herein contained, the parties hereto agree as follows:


Section 1.              AMENDMENTS TO THE CREDIT
AGREEMENT


1.1          Amendments to Article VI:
Affirmative Covenants


A.            Section 6.12(a) of the Credit Agreement is hereby
amended by deleting clause (iv) in its entirety and substituting the following
therefor:


“(iv) (A) up to an
aggregate of $13,400,000 in Restricted Payments made in cash in the fiscal
years ending December 31, 2005 and December 31, 2006 to the extent allowed by Section
7.6(d)(i), and (B) up to an aggregate of $36,600,000 in Restricted Payments
made in cash in the period beginning on January 1, 2007 and ending on the
Maturity Date to the extent allowed by Section 7.6(d)(ii).”


1.2          Amendment to Article VII:
Negative Covenants


Section
7.6 of the Credit Agreement is hereby amended by deleting paragraph (d) thereof
and substituting the following therefor:


“(d)
so long as no Default or Event of Default shall have occurred and is continuing
or shall be caused thereby, Borrower may purchase, redeem or otherwise acquire
shares of its common stock or other common equity interests for cash
consideration not exceeding (i) $13,400,000 in the aggregate during the fiscal
years ending December 31, 2005 and December 31, 2006, and (ii) $36,600,000 in
the aggregate during the period beginning on January 1, 2007 and ending on the
Maturity Date (exclusive of any amount described in clause (i) above).”



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Section 2.              CONDITIONS TO EFFECTIVENESS


Section 1
of this Amendment shall become effective only upon the satisfaction of all of
the following conditions precedent (the date of satisfaction of such conditions
being referred to herein as the “Third Amendment Effective
Date”):


A.            On or before the Third Amendment Effective Date,
Borrower shall deliver to Lenders (or to Agent for Lenders with sufficient
originally executed copies, where appropriate, for each Lender and its counsel)
executed copies of this Amendment executed by Borrower and each Guarantor.


B.            On or before the Third Amendment Effective Date, all
corporate and other proceedings taken or to be taken in connection with the
transactions contemplated hereby and all documents incidental thereto not
previously found acceptable by Agent, acting on behalf of Lenders, and its
counsel shall be satisfactory in form and substance to Agent and such counsel,
and Agent and such counsel shall have received all such counterpart originals
or certified copies of such documents as Agent may reasonably request.


Section 3.              BORROWER’S REPRESENTATIONS AND
WARRANTIES


In
order to induce Lenders to enter into this Amendment and to amend the Credit
Agreement in the manner provided herein, Borrower represents and warrants to
each Lender that the following statements are true, correct and complete:


A.            Corporate Power and Authority. 
Each Loan Party has all requisite corporate power and authority to enter
into this Amendment and to carry out the transactions contemplated by, and
perform its obligations under, the Credit Agreement as amended by this Amendment
(the “Amended Agreement”) and the other Loan
Documents.


B.            Authorization of Agreements. 
The execution and delivery of this Amendment and the performance of the
Amended Agreement have been duly authorized by all necessary corporate action
on the part of each Loan Party.


C.            No Conflict. 
The execution and delivery by each Loan Party of this Amendment and the
performance by such Loan Party of the Amended Agreement and the other Loan
Documents do not and will not (i) violate any provision of any law or any
governmental rule or regulation applicable to such Loan Party or any of its
Subsidiaries, the Certificate or Articles of Incorporation or Bylaws of such
Loan Party or any of its Subsidiaries or any order, judgment or decree of any
court or other agency of government binding on such Loan Party or any of its
Subsidiaries, (ii) conflict with, result in a breach of or constitute (with due
notice or lapse of time or both) a default under any Contractual Obligation of
such Loan Party or any of its Subsidiaries, (iii) result in or require the
creation or imposition of any Lien upon any of the properties or assets of such
Loan Party or any of its Subsidiaries (other than Liens created under any of
the Loan Documents in favor of Agent on behalf of Lenders), or (iv) require
any approval of stockholders or any approval or consent of any Person under any
Contractual Obligation of such Loan Party or any of its Subsidiaries.


D.            Governmental Consents. 
The execution and delivery by Borrower and Guarantors of this Amendment
and the performance by Borrower and Guarantors of the Amended Agreement and the
other Loan Documents do not and will not require any registration with, consent
or approval of, or notice to, or other action to, with or by, any federal,
state or other governmental authority or regulatory body.



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E.             Binding Obligation. 
This Amendment has been duly executed and delivered by each Loan Party
and this Amendment and the Amended Agreement are the legally valid and binding
obligations of such Loan Party, enforceable against such Loan Party in
accordance with their respective terms, except as may be limited by bankruptcy,
insolvency, reorganization, moratorium or similar laws relating to or limiting
creditors’ rights generally or by equitable principles relating to
enforceability.


F.             Incorporation of Representations
and Warranties From Credit Agreement.  The
representations and warranties contained in Section 5 of the Credit
Agreement are and will be true, correct and complete in all material respects
on and as of the Third Amendment Effective Date to the same extent as though
made on and as of that date, except to the extent such representations and
warranties specifically relate to an earlier date, in which case they were
true, correct and complete in all material respects on and as of such earlier
date.


G.            Absence of Default. 
No event has occurred and is continuing or will result from the
consummation of the transactions contemplated by this Amendment that would
constitute a Default or an Event of Default.


Section 4.              MISCELLANEOUS


A.            Reference to and Effect on the
Credit Agreement and the Other Loan Documents.


(i)            On and after the Third Amendment Effective Date, each
reference in the Credit Agreement to “this Agreement”, “hereunder”, “hereof”,
“herein” or words of like import referring to the Credit Agreement, and each
reference in the other Loan Documents to the “Credit Agreement”, “thereunder”,
“thereof” or words of like import referring to the Credit Agreement shall mean
and be a reference to the Amended Agreement.


(ii)           Except as specifically amended by this Amendment, the
Credit Agreement and the other Loan Documents shall remain in full force and
effect and are hereby ratified and confirmed.


(iii)          The execution, delivery and performance of this
Amendment shall not, except as expressly provided herein, constitute a waiver
of any provision of, or operate as a waiver of any right, power or remedy of
Agent or any Lender under, the Credit Agreement or any of the other Loan
Documents.


B.            Fees and Expenses. Borrower acknowledges that all costs,
fees and expenses as described in Section 10.4 of the Credit Agreement
incurred by Agent and its counsel with respect to this Amendment and the
documents and transactions contemplated hereby shall be for the account of Borrower.


C.            Headings. 
Section and subsection headings in this Amendment are included
herein for convenience of reference only and shall not constitute a part of
this Amendment for any other purpose or be given any substantive effect.


D.            Applicable Law.  THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS
OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY, AND SHALL BE CONSTRUED AND
ENFORCED IN ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF CALIFORNIA
(INCLUDING WITHOUT LIMITATION SECTION 1646.5 OF THE CIVIL 



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CODE OF THE STATE OF CALIFORNIA),
WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES.


E.             Counterparts; Effectiveness. 
This Amendment may be executed in any number of counterparts and by
different parties hereto in separate counterparts, each of which when so
executed and delivered shall be deemed an original, but all such counterparts
together shall constitute but one and the same instrument; signature pages may
be detached from multiple separate counterparts and attached to a single
counterpart so that all signature pages are physically attached to the same
document.  This Amendment (other than the
provisions of Section 1 hereof, the effectiveness of which is governed by
Section 2 hereof) shall become effective upon the execution of a
counterpart hereof by Borrower and Required Lenders and receipt by Borrower and
Agent of written or telephonic notification of such execution and authorization
of delivery thereof.


Section 5.              ACKNOWLEDGEMENT AND CONSENT BY
GUARANTORS


Each
Guarantor hereby acknowledges that it has read this Amendment and consents to
the terms thereof, and hereby confirms and agrees that, notwithstanding the
effectiveness of this Amendment, the obligations of each Guarantor under its
applicable Guaranty and the Collateral Documents shall not be impaired or affected
and the applicable Guaranty and the Collateral Documents are, and shall
continue to be, in full force and effect and is hereby confirmed and ratified
in all respects.  Each Guarantor further
agrees that nothing in the Credit Agreement, this Amendment or any other Loan
Document shall be deemed to require the consent of such Guarantor to any future
amendment to the Credit Agreement.



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IN
WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed and delivered by their respective officers
thereunto duly authorized as of the date first written above.


	
  

  	
  BORROWER:

  
	
   

  	
  QUIDEL CORPORATION

  
	
   

  	
  By: 

  	
  /s/ Caren L. Mason

  	
   

  
	
   

  	
  Title: President/CEO

  
	
   

  	
  Name:  Caren
  L. Mason

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  GUARANTORS:

  
	
   

  	
   

  
	
   

  	
  PACIFIC BIOTECH, INC.

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Caren L. Mason

  	
   

  
	
   

  	
  Title: President

  
	
   

  	
  Name:  Caren
  L. Mason

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  METRA BIOSYSTEMS, INC.

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Caren L. Mason

  	
   

  
	
   

  	
  Title: President

  
	
   

  	
  Name:  Caren
  L. Mason

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  OSTEO SCIENCES CORPORATION

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Caren L. Mason

  	
   

  
	
   

  	
  Title: President

  
	
   

  	
  Name:  Caren
  L. Mason

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  LITMUS CONCEPTS, INC.

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Caren L. Mason

  	
   

  
	
   

  	
  Title: President

  
	
   

  	
  Name:  Caren
  L. Mason

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  BANK OF AMERICA, N.A., as Agent

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Patrick Loughlin

  	
   

  
	
   

  	
  Title: Senior Vice President

  
	
   

  	
  Name:  Patrick
  Loughlin

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  BANK OF AMERICA, N.A., as Lender

  
	
   

  	
   

  
	
   

  	
   

  
	
   

  	
  By: 

  	
  /s/ Patrick Loughlin

  	
   

  
	
   

  	
  Title: Senior Vice President

  
	
   

  	
  Name:  Patrick
  Loughlin

  



 


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