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                                                                     EXHIBIT 4.5

                           PATHOGENESIS CORPORATION
                        1999 EMPLOYEE STOCK OPTION PLAN
                                        

     1.   Purpose.  The PathoGenesis Corporation 1999 Employee Stock Option Plan
(the "Plan") is intended to promote the interests of PathoGenesis Corporation
("PathoGenesis") and its shareholders by providing employees (other than any
employee who is an officer or director of PathoGenesis), consultants,
independent contractors and other agents of the Company (as defined below) with
appropriate incentives and rewards to attract and retain their services and to
encourage them to acquire a proprietary interest in the long-term success of the
Company. This Plan provides for the granting of stock options that are not
"incentive stock options" within the meaning of Section 422 of the Internal
Revenue Code.

     2.   Definitions.  As used in the Plan:

     (a)  "Agreement" shall mean a written agreement between PathoGenesis and a
Participant evidencing an Option.

     (b)  "Board" shall mean the board of directors of PathoGenesis.

     (c)  "Committee" shall mean the Compensation and Nominating Committee of
the Board or such other committee as the Board may authorize to administer the
Plan.

     (d)  "Common Stock" shall mean common stock, par value $.001 per share, of
PathoGenesis, or any security substituted for such stock pursuant to Section
3.2.

     (e)  "Company" shall mean PathoGenesis and shall include any business
entity that controls, is controlled by, or is under common control with,
PathoGenesis.

     (f)  "Fair Market Value" per share of Common Stock shall mean (1) the
closing sale price per share of Common Stock on the national securities exchange
on which such stock is principally traded for the date in question on which
there was a reported sale of such stock on such exchange (or, if no sales of
Common Stock were made on that date, the closing sale price as reported for the
most recent preceding day on which there was a reported sale of such stock), or
(2) if the Common Stock is not then traded on a national securities exchange,
the closing sale price per share of Common Stock as reported on the Nasdaq Stock
Market for the date in question (or, if no sales of Common Stock were made on
that date, the closing sale price as reported for the most recent preceding day
on which there was a reported sale of such stock), or (3) if the shares of
Common Stock are not then listed on a national securities exchange or traded in
an over-the-counter market or the value of such shares is not otherwise readily
ascertainable, such value as determined by the Committee in good faith.

     (g)  "Option" shall mean a stock option to purchase shares of Common Stock
granted under the Plan and shall be "non-qualified" for purposes of Section 421
or 422 of the Internal Revenue Code.

     (h)  "Participant" shall mean the recipient of a grant of an Option under
the Plan or, upon such recipient's death, his or her successors, heirs,
executors or administrators, as the case may be.

     (i)  "Securities Act" shall mean the Securities Act of 1933, as amended.
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     3.   Shares Subject to the Plan.

     3.1  Shares Available.  The maximum number of shares of Common Stock
reserved for issuance under the Plan shall be equal to the sum (subject to
adjustment as provided herein) of: (i) 600,000 shares and (ii) shares (a)
purchased or acquired by PathoGenesis using amounts equivalent to the cash
proceeds received by PathoGenesis or (b) tendered to or withheld by
PathoGenesis, in either case (ii)(a) or (ii)(b) in connection with the exercise
of Options granted under this Plan. Such shares may be authorized but unissued
Common Stock or authorized and issued Common Stock held in PathoGenesis'
treasury. For purposes of determining the number of shares of Common Stock
issued under the Plan, no shares shall be deemed issued until they are actually
delivered to a Participant, or such other person in accordance with Section 13.
Shares covered by Options granted under the Plan that either wholly or in part
are not earned, or that expire or are forfeited, terminated, cancelled or
exchanged for other Options, shall be available for future issuance under the
Plan.

     3.2  Adjustment to Reflect Capital Changes.  In the event that the
Committee shall determine that any dividend or other distribution (whether in
the form of cash, Common Stock, or other property), recapitalization, stock
split, reverse stock split, reorganization, merger, consolidation, spin-off,
combination, repurchase, or share exchange, or other similar corporate action or
event affects the Common Stock such that an adjustment is appropriate in order
to prevent dilution or enlargement of the rights of Participants under the Plan,
then the Committee shall make such equitable changes or adjustments as it deems
necessary or appropriate to any or all of (a) the number and kind of securities
that may then be issued in connection with Options, (b) the number and kind of
securities issued or issuable in respect of outstanding Options, (c) the option
exercise price relating to any Option, and (d) the maximum number of shares
issuable under the Plan.

     4.   Administration of the Plan.

     4.1  The Committee.  The Plan shall be administered by the Committee. The
Committee shall have full power and authority, subject to and not inconsistent
with the express provisions of the Plan, to (a) select persons to whom Options
from time to time may be granted under the Plan, (b) determine the number of
shares of Common Stock to be covered by each Option granted, (c) determine the
terms and conditions, not inconsistent with the provisions of the Plan, of any
Option granted, (d) determine whether, to what extent and under what
circumstances Options may be cancelled or suspended, (e) interpret and
administer the Plan and any instrument or agreement entered into under the Plan,
(f) establish such rules and regulations and appoint such agents as it shall
deem appropriate for the proper administration of the Plan, and (g) make any
other determination and take any other action that it deems necessary or
desirable for administration of the Plan. Decisions of the Committee shall be
final, conclusive and binding upon all interested parties. A majority vote of
the members of the Committee present at a meeting of the Committee may determine
its actions. Any decision or determination reduced to writing and signed by all
of the members shall be fully as effective as if it had been made at a meeting
duly called and held.

     4.2  Delegation.  The Committee may delegate to the Chief Executive Officer
of the PathoGenesis (or to such other officer or officers of PathoGenesis as the
Chief Executive Officer may designate, acting under his supervision), subject to
such limitations as the Committee may determine, the right to grant Options to
eligible Participants; provided, however, that no Option shall be granted
pursuant to such delegation to any person to whom the Committee could not have
granted an Option.

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     5.   Eligibility.  The Committee shall have sole discretion to determine
persons who shall be eligible to participate in the Plan. Unless otherwise
determined by the Committee, all regular full-time employees in permanent
positions (other than any employee who is an officer or director of
PathoGenesis), consultants, independent contractors and other agents of the
Company shall be eligible to receive grants under the Plan.

     6.   Terms and Conditions of Options.

     6.1  Agreements.  Each Option shall be evidenced by an Agreement which
shall contain such provisions as the Committee may in its sole discretion deem
necessary or desirable. By accepting an Option, a Participant thereby agrees
that the Option shall be subject to all of the terms and provisions of the Plan
and the applicable Agreement.

     6.2  Exercise Price.  Each Agreement shall set forth the option exercise
price payable by the Participant to PathoGenesis upon exercise of the Option.
The exercise price per share shall be determined by the Committee; provided,
however, that the exercise price shall in no event be less than the Fair Market
Value per share of Common Stock on the date of grant.

     6.3  Replenishment Options.  The Committee shall have the authority to
specify, at or after the time of grant, that a Participant shall be granted a
new Option (a "Replenishment Option") for a number of shares equal to the number
of shares surrendered by the Participant upon exercise of all or a part of a
stock option, subject to the availability of shares of Common Stock under the
Plan at the time of such exercise. Each Replenishment Option shall cover a
number of shares of Common Stock equal to the number of shares of Common Stock
surrendered in payment of the exercise price under the original Option or
withheld (and, if so determined by the Committee, to satisfy tax withholding
obligations) resulting from the exercise of the original Option, shall have an
option exercise price per share equal to the Fair Market Value per share of
Common Stock on the date of grant of such Replenishment Option, shall expire on
the stated expiration date of the original Option, and shall be subject to such
conditions as may be specified by the Committee in its discretion, subject to
the terms of the Plan.

     7.   Exercise of An Option.

     7.1  Exercising An Option; Payment of Exercise Price.  A Participant may
exercise an Option for all or any portion of the shares as to which the Option
is exercisable. In its sole discretion, the Committee may establish from time
to time administrative procedures, consistent with the Plan, for the exercise of
Options. A Participant exercising an Option shall pay in full the exercise
price in cash at the time of the exercise or, to the extent permitted by law and
as permitted by the Committee from time to time, by other means, including (i)
tendering Common Stock (which, if not purchased on the open market, the
Participant must have held for at least six months), (ii) authorizing a third
party to sell shares (or a sufficient portion thereof) acquired upon exercise of
the Option and to remit to PathoGenesis a sufficient portion of the sale
proceeds to pay for all the shares acquired through such exercise and any tax
withholding obligations resulting from such exercise, or (iii) any combination
of (i) and (ii). The Committee shall determine acceptable methods of tendering
Common Stock to exercise an Option as it deems appropriate. For the purpose of
assisting an optionee to exercise an Option, the Company may make loans to the
optionee on such terms and conditions as the Committee may authorize.

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     7.2  Withholding Tax.  Whenever cash is to be paid pursuant to an Option,
the Company shall have the right to deduct therefrom an amount sufficient to
satisfy any federal, state and local withholding tax requirements related
thereto. Whenever shares of Common Stock are to be delivered pursuant to an
Option, the Company shall have the right to require the Participant to remit to
the Company in cash an amount sufficient to satisfy any federal, state and local
withholding tax requirements related thereto. The Committee may require a
Participant to, or with the approval of the Committee a Participant may, satisfy
the foregoing requirement by electing to have PathoGenesis withhold from
delivery shares of Common Stock having a value equal to the amount of tax to be
withheld, which shall not exceed the amount computed at the minimum required
withholding rate. Such shares shall be valued at the Fair Market Value per share
of Common Stock on the date as of which the amount of tax to be withheld is
determined. Fractional share amounts shall be settled in cash. Such a
withholding election may be made with respect to all or any portion of the
shares of Common Stock to be delivered pursuant to an Option.

     8.   Rights As Shareholder.  No person shall have any rights as a
shareholder with respect to any shares of Common Stock covered by or relating to
any Option until the date of issuance of a stock certificate for such shares.
Except as otherwise expressly provided in Section 3.3, no adjustment to any
Option shall be made for dividends or other rights for which the record date
occurs prior to the date such stock certificate is issued.

     9.   No Special Employment Rights; No Right to Option Grants.  Nothing
contained in the Plan or any Agreement shall confer upon any Participant any
right to the continuation of employment or engagement by the Company or
interfere in any way with the right of the Company, subject to the terms of any
separate employment or engagement agreement, at any time to terminate the
relationship or to increase or decrease the compensation of the Participant. No
person shall have any right to receive an Option hereunder, and there is no
obligation for uniformity of treatment for Participants. The Committee's
granting of an Option to a Participant at any time shall neither require the
Committee to grant any other Option to such Participant or any other person at
any time, or preclude the Committee from making subsequent grants to such
Participant or any other person.

     10.  Securities Law Matters.

     10.1 Registration of Securities; Issuance of Certificates.  PathoGenesis
shall be under no obligation to effect the registration pursuant to the
Securities Act of any interests in the Plan or any shares of Common Stock to be
issued hereunder or to effect similar compliance under any state laws.
Notwithstanding anything herein to the contrary, PathoGenesis shall not be
obliged to cause to be issued or delivered any certificates evidencing shares of
Common Stock pursuant to the Plan unless and until PathoGenesis is advised by
its counsel that the issuance and delivery of such certificates is in compliance
with all applicable laws, regulations of governmental authority and the
requirements of any securities exchange on which shares of Common Stock are
traded. The Committee may require, as a condition of the issuance and delivery
of certificates evidencing shares of Common Stock pursuant to the terms hereof,
that the recipient of such certificates make such agreements and
representations, and that such certificates bear such legends, as the Committee,
in its sole discretion, deems necessary or desirable.

     10.2 Deferred Issuance or Transfer.  The transfer of any shares of Common
Stock hereunder shall be effective only at such time as counsel to PathoGenesis
shall have 

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determined that the issuance and delivery of such shares is in compliance with
all applicable laws, regulations of governmental authority and the requirements
of any securities exchange on which shares of Common Stock are traded. The
Committee may, in its sole discretion, defer the effectiveness of any transfer
of shares of the Common Stock hereunder in order to allow the issuance of such
shares to be made pursuant to registration or an exemption from registration or
other methods for compliance available under federal or state securities laws.
The Committee shall inform the Participant in writing of its decision to defer
the effectiveness of a transfer. During the period of such deferral in
connection with the exercise of an Option, the Participant may, by written
notice, withdraw such exercise and obtain a refund of any amount paid with
respect thereto.

     11.  Amendment or Termination.  The Board may, at any time, amend, suspend
or terminate the Plan, provided that no such amendment, suspension or
termination shall be made without the consent of the affected Participant, if
such action would impair the rights of the Participant under any outstanding
Option.

     The Committee may amend the terms of any outstanding Option, prospectively
or retroactively, but no such amendment shall impair the rights of any
Participant without his or her consent. Notwithstanding any provision of the
Plan, the Committee may not amend the terms of any Option to reduce the option
exercise price.

     12.  Grants to Foreign Nationals.  Options may be granted to employees,
consultants, independent contractors and other agents who are foreign nationals
or employed outside the United states, or both, on such terms and conditions
different from those applicable to grants to Participants in the United States
as may, in the judgment of the Committee, be necessary or desirable in order to
recognize differences in local law or tax policy. The Committee also may impose
conditions on the exercise or vesting of Options in order to minimize
PathoGenesis' obligation with respect to tax equalization for employees on
assignments outside their home country.

     13.  Transfers of Options.  Unless otherwise determined by the Committee
and set forth in the Agreement, no Option granted under the Plan shall be
assignable, transferable or payable to or exercisable by anyone other than the
Participant to whom it was granted, except for transfer to the estate of or
successors to a Participant upon his or her death.

     14.  Expenses and Receipts.  The expenses of the Plan shall be paid by
PathoGenesis. Any proceeds received by PathoGenesis in connection with any
Option will be used for general corporate purposes.

     15.  Effective Date and Term of Plan.  The Plan shall become effective on
the date it is adopted by the Board. The Plan shall remain in effect in
accordance with its terms, unless amended or terminated by the Board. Options
outstanding at Plan termination will remain in effect according to their terms
and the provisions of the Plan.

     16.  Applicable Law.  Except to the extent preempted by any applicable
federal law, the Plan will be construed and administered in accordance with the
laws of the State of Delaware, without reference to its principles of conflicts
of law.

     17.  No Fractional Shares.  No fractional shares of Common Stock shall be
issued or delivered pursuant to the Plan. The Committee shall determine whether
cash or other

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property shall be issued or paid in lieu of such fractional shares or whether
such fractional shares or any rights thereto shall be forfeited or otherwise
eliminated.

     18.  Severability.  If any provision of the Plan is held to be invalid or
unenforceable, the other provisions of the Plan shall not be affected but shall
be applied as if the invalid or unenforceable provision had not been included in
the Plan.


     Approved by the Board of Directors on April 13, 1999.

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