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[PATHOGENESIS LETTERHEAD]
August 21, 2000
Dear Stockholder:
I am pleased to inform you that PathoGenesis Corporation has entered into a
merger agreement with Chiron Corporation ("Chiron"), pursuant to which a wholly
owned subsidiary of Chiron has commenced a tender offer to purchase all of the
outstanding shares of PathoGenesis's common stock for $38.50 per share in cash.
The tender offer is conditioned upon, among other things, a majority of
PathoGenesis's shares outstanding on a fully diluted basis being tendered and
not withdrawn and the receipt of regulatory approvals. The tender offer will be
followed by a merger, in which each share of PathoGenesis common stock not
purchased in the tender offer will be converted into the right to receive in
cash the price paid in the tender offer.
YOUR BOARD OF DIRECTORS HAS DETERMINED THAT THE MERGER AGREEMENT, THE CHIRON
OFFER AND THE MERGER ARE ADVISABLE AND IN THE BEST INTERESTS OF PATHOGENESIS'S
STOCKHOLDERS, AND UNANIMOUSLY RECOMMENDS THAT PATHOGENESIS'S STOCKHOLDERS ACCEPT
THE CHIRON OFFER AND TENDER THEIR SHARES OF PATHOGENESIS COMMON STOCK PURSUANT
TO THE OFFER.
In arriving at its recommendation, the Board of Directors considered a
number of factors, as described in the attached Schedule 14D-9, including the
opinion of the Company's financial advisor, Goldman, Sachs & Co., that, as of
the date of the opinion, and based upon and subject to the matters set forth
therein, the consideration to be received by the holders of PathoGenesis common
stock in the offer and the merger is fair from a financial point of view to
PathoGenesis's stockholders. A copy of Goldman, Sachs & Co.'s written opinion,
which sets forth the assumptions made, procedures followed and matters
considered by Goldman, Sachs & Co. in rendering its opinion, can be found in
Exhibit (a)(4) to the Schedule 14D-9. You should read the opinion carefully and
in its entirety.
Enclosed are the Chiron Offer to Purchase, dated August 21, 2000, the Letter
of Transmittal and related documents. These documents set forth the terms and
conditions of the tender offer. The Schedule 14D-9 describes in more detail the
reasons for your Board's conclusions and contains other information relating to
the tender offer. We urge you to consider this information carefully.
/s/ WILBUR H. GANTZ
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Wilbur H. Gantz
Chairman and
Chief Executive Officer
