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                                                                    June 9, 1999

To Our Shareholders:

    I am pleased to inform you that on June 4, 1999, Metra Biosystems entered
into an Agreement and Plan of Merger with Quidel Corporation and MBS Acquisition
Corporation, a wholly-owned subsidiary of Quidel. Under the Agreement, Quidel
has commenced a cash tender offer to purchase all of the outstanding shares of
Metra's Common Stock for $1.78 per share (including the associated Preferred
Shares Purchase Rights), without interest. The offer will be followed by a
Merger in which any remaining shares of Metra's Common Stock will be converted
into the right to receive $1.78 per share in cash, without interest.

    YOUR BOARD OF DIRECTORS HAS UNANIMOUSLY APPROVED (EXCEPT FOR DR. POLAN WHO
IS ALSO A DIRECTOR OF QUIDEL AND, ACCORDINGLY, DID NOT VOTE) THE OFFER, THE
MERGER, THE STOCK OPTION AGREEMENT, THE INDEMNIFICATION AGREEMENT AND THE MERGER
AGREEMENT AS DESCRIBED IN THE SCHEDULE 14D-9 ATTACHED HERETO AND DETERMINED THAT
THE OFFER, THE MERGER, THE STOCK OPTION AGREEMENT AND THE MERGER AGREEMENT ARE
FAIR TO AND IN THE BEST INTERESTS OF THE SHAREHOLDERS OF THE COMPANY AND
RECOMMENDS THAT THE SHAREHOLDERS OF THE COMPANY ACCEPT THE OFFER AND TENDER
THEIR SHARES TO PURCHASER PURSUANT TO THE OFFER.

    In arriving at its recommendation, the Board of Directors gave consideration
to a number of factors, which are described in the attached Schedule 14D-9 that
has been filed today with the Securities and Exchange Commission. These factors
include, among other things, the opinion of EGS Securities Corp., the Company's
financial advisor, that the consideration to be received by the shareholders of
the Company in the Offer and Merger pursuant to the Agreement is fair from a
financial point of view to the shareholders of the Company (other than Quidel
and its affiliates).

    In addition to the attached Schedule 14D-9 relating to the Offer, also
enclosed is the Offer to Purchase, dated June 9, 1999, of Quidel, together with
related materials to be used for tendering your shares. These documents set
forth the terms and conditions of the Offer and the Merger and provide
instructions as to how to tender your shares. I urge you to read the enclosed
materials carefully.

                                          Sincerely,

                                          /s/ George W. Dunbar, Jr.

                                          George W. Dunbar, Jr.

                                          PRESIDENT AND CHIEF EXECUTIVE OFFICER