XENOPORT, INC. CHANGE OF CONTROL AGREEMENT

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Exhibit 10.15

XENOPORT, INC.

CHANGE OF CONTROL AGREEMENT

This Change of Control Agreement (the "AGREEMENT") is made and entered

into by and between William J. Rieflin (the "EXECUTIVE") and XenoPort, Inc. a

Delaware corporation (the "COMPANY"), effective as of June 18, 2004.

RECITALS

It is expected that the Company from time to time may consider the

possibility of an acquisition by another company or other change of control. The

Board of Directors of the Company (the "BOARD") recognizes that such

consideration can be a distraction to the Executive and can cause the Executive

to consider alternative employment opportunities. The Board has determined that

it is in the best interests of the Company and its stockholders to assure that

the Company will have the continued dedication and objectivity of the Executive,

notwithstanding the possibility, threat or occurrence of a Change of Control (as

defined below) of the Company.

The Board believes that it is in the best interests of the Company and its

stockholders to provide the Executive with an incentive to continue his

employment and to motivate the Executive to maximize the value of the Company

upon a Change of Control for the benefit of its stockholders.

Certain capitalized terms used in the Agreement are defined in Section 5

below.

The parties hereto agree as follows:

1. TERM OF AGREEMENT. This Agreement shall terminate upon the date that all

obligations of the parties hereto with respect to this Agreement have been

satisfied.

2. AT-WILL EMPLOYMENT. The Company and the Executive acknowledge that the

Executive's employment is and shall continue to be at-will. If the Executive's

employment terminates for any reason, including (without limitation) any

termination prior to a Change of Control, the Executive shall not be entitled to

any payments, benefits, damages, awards or compensation other than as provided

by this Agreement, or as may otherwise be available in accordance with the

Company's established written Executive plans or pursuant to other written

agreements with the Company.

3. TERMINATION FOLLOWING A CHANGE OF CONTROL.

(a) TERMINATION WITHOUT CAUSE OR VOLUNTARY TERMINATION FOR GOOD REASON. In

the event that a Change of Control (as defined below) of the Company occurs, and

during the period beginning on the closing date of the transaction giving rise

to such Change of Control and ending twelve (12) months after such closing date,

the Executive's employment with the Company (or the successor entity in such

Change of Control transaction) is either (1) terminated by the Company (or its

successor entity) without Cause (as defined below) or (2) terminated by the

Executive for Good Reason (as defined below), then the Executive shall be

entitled to receive Termination Benefits (as defined below).

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(b) CONSTRUCTIVE TERMINATION. In the event that a Change of Control (as

defined below) of the Company occurs, and during the period beginning on the

closing date of the transaction giving rise to such Change of Control and ending

twelve (12) months after such closing date, the Executive's employment with the

Company (or the successor entity in such Change of Control transaction) is

Constructively Terminated (as defined below) by [he Executive, then the

Executive shall be entitled to receive Termination Benefits (as defined below).

Notwithstanding the foregoing, the Executive shall not be entitled to the

Termination Benefits solely by reason of this Section 3(b) if the Executive

resigns his employment prior to the date six (6) months after the closing of the

transaction giving rise to such Change of Control.

4. CERTAIN ADDITIONAL PAYMENTS BY THE COMPANY.

(a) In the event that it shall be determined (as hereafter provided) that

any payment or distribution by the Company or any of its affiliates to or for

the benefit of the Executive, whether paid or payable or distributed or

distributable pursuant to the terms of this Agreement or otherwise pursuant to

or by reason of any other agreement, policy, plan, program or arrangement,

including without limitation any stock option, stock appreciation right or

similar right, or the lapse or termination of any restriction on or the vesting

or exercisability of any of the foregoing (a "PAYMENT"), would be subject to the

excise tax imposed by Section 4999 of the Internal Revenue Code of 1986, as

amended (the "CODE") (or any successor provision thereto) by reason of being

considered "contingent on a change in ownership or control" of the Company,

within the meaning of Section 280G of the Code (or any successor provision

thereto) or to any similar tax imposed by state or local law, or any interest or

penalties with respect to such tax (such tax or taxes, together with any such

interest and penalties, being hereafter collectively referred to as the "EXCISE

TAX"), then the Executive shall be entitled to receive an additional payment or

payments (collectively, a "GROSS-UP PAYMENT"); provided, however, that no

Gross-Up Payment shall be made with respect to the Excise Tax, if any,

attributable to (i) any incentive stock option, as defined by Section 422 of the

Code ("ISO") granted prior to the execution of this Agreement, (ii) any stock

appreciation or similar right, whether or not limited, granted in tandem with

any IS0 described in clause (i), or (iii) any stock, stock option, stock

appreciation or similar right, or other Stock Right OTHER THAN those acquired by

the Executive at the time of Executive's commencement of employment with the

Company. The Gross-Up Payment shall be in an amount such that, after payment by

the Executive of all taxes (including any interest or penalties imposed with

respect to such [axes), including any Excise Tax imposed upon the Gross-Up

Payment, the Executive retains an amount of the Gross-Up Payment equal to the

Excise Tax imposed upon the Payment. Notwithstanding anything to the contrary

set forth in this Agreement, in no event shall the aggregate Gross-Up Payment

payable by the Company hereunder exceed $1,500,000.

(b) Subject to the provisions of Section 4(b), all determinations required

to be made under this Section 4, including whether an Excise Tax is payable by

the Executive and the amount of such Excise Tax and whether a Gross-Up Payment

is required to be paid by the Company to the Executive and the amount of such

Gross-Up Payment, if any, shall be made by a nationally recognized accounting

firm (the "ACCOUNTING FIRM") selected by the Company with the consent of the

Executive, which shall not unreasonably be withheld. The Executive shall direct

the Accounting Firm to submit its determination and detailed supporting

calculations to both the Company and the Executive within 30 calendar days after

the Termination Date, if

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applicable, and any such other time or times as may be requested by the Company

or the Executive. If the Accounting Firm determines that any Excise Tax is

payable by the Executive, the Company shall pay the required Gross-Up Payment to

the Executive within five business days after receipt of such determination and

calculations with respect to any Payment to the Executive. If the Accounting

Firm determines that no Excise Tax is payable by the Executive, it shall, at the

same time as it makes such determination, furnish the Company and the Executive

an opinion that the Executive has substantial authority not to report any Excise

Tax on his federal, state or local income or other tax return. As a result of

the uncertainty in the application of Section 4999 of the Code (or any successor

provision thereto) and the possibility of similar uncertainty regarding

applicable state or local tax law at the time of any determination by the

Accounting Firm hereunder, it is possible that Gross-Up Payments which will not

have been made by the Company should have been made (an "UNDERPAYMENT"),

consistent with the calculations required to be made hereunder. In the event

that the Company exhausts or fails to pursue its remedies pursuant to Section

4(f) and the Executive thereafter is required to make a payment of any Excise

Tax, the Executive shall direct the Accounting Firm to determine the amount of

the Underpayment that has occurred and to submit its determination and detailed

supporting calculations to both the Company and the Executive as promptly as

possible. Any such Underpayment shall be promptly paid by the Company to, or for

the benefit of, the Executive within five business days after receipt of such

determination and calculations.

(c) The Company and the Executive shall each provide the Accounting Firm

access to and copies of any books, records and documents in the possession of

the Company or the Executive, as the case may be, reasonably requested by the

Accounting Firm, and otherwise cooperate with the Accounting Firm in connection

with the preparation and issuance of the determinations and calculations

contemplated by Section 4(b). Any determination by the Accounting Firm as to the

amount of the Gross-Up Payment shall be binding upon the Company and the

Executive.

(d) The federal, state and local income or other tax returns filed by the

Executive shall be prepared and filed on a consistent basis with the

determination of the Accounting Firm with respect to the Excise Tax payable by

the Executive. The Executive shall make proper payment of the amount of any

Excise Payment, and at the request of the Company, provide to the Company true

and correct copies (with any amendments) of his federal income tax return as

filed with the Internal Revenue Service and corresponding state and local tax

returns, if relevant, as filed with the applicable taxing authority, and such

other documents reasonably requested by the Company, evidencing suc