<PAGE>




                                                                   Exhibit 10.10


                              EMPLOYMENT AGREEMENT
                                 ROBERT S. BROWN


         THIS EMPLOYMENT AGREEMENT (the "Agreement") is entered into this 27th
day of November 2006 (the "Effective Date") by and between NxStage Medical, Inc.
(the "Company"), a Delaware corporation with its principal place of business at
439 South Union Street, Lawrence, MA 01843 and Robert S. Brown (the
"Executive").

         WHEREAS, the Company desires to employ Executive, and Executive desires
to be employed by the Company upon the terms and conditions hereinafter set
forth;

         NOW, THEREFORE, the parties hereto, intending to be legally bound,
hereby agree as follows:

1.       Employment. The Company hereby agrees to employ Executive, and
Executive hereby accepts such employment and agrees to perform Executive's
duties and responsibilities, in accordance with the terms, conditions and
provisions hereinafter set forth. This Agreement shall be effective as of the
Effective Date and shall continue until terminated in accordance with Section 2
hereof. Nothing in this Agreement shall be construed as giving Executive any
right to be retained in the employ of the Company, and Executive specifically
acknowledges that Executive shall be an employee-at-will of the Company, and
thus subject to discharge at any time by the Company with or without cause and
without compensation of any nature except as provided in Section 2 below.

         1.1      Duties and Responsibilities. Executive shall serve as Senior
Vice President and Chief Financial Officer of the Company and shall perform all
duties and accept all responsibilities incident to such position as may be
reasonably assigned to Executive by the Company's Board of Directors (the
"Board") or by the Chief Executive Officer ("CEO") of the Company. Executive
shall be based at the Company's headquarters in Massachusetts, or such place or
places in the continental United States as the Board shall determine.

         1.2      Extent of Service. Executive agrees to use Executive's best
efforts to carry out Executive's duties and responsibilities under Section 1.1
hereof and, consistent with the other provisions of this Agreement, to devote
substantially all of Executive's business time, attention and energy thereto.
The foregoing shall not be construed as preventing Executive from making passive
investments in other businesses or enterprises, provided that Executive agrees
not to become engaged in any other business activity which, in the reasonable
judgment of the Board, is likely to interfere with Executive's ability to
discharge Executive's duties and responsibilities to the Company. The foregoing
shall also not be construed as preventing Executive from participating as a
member of a board of directors or in some other capacity with another
organization, including a public company, provided that Executive shall have
received prior approval of the Board.


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         1.3      Base Salary. For all the services rendered by Executive
hereunder, the Company shall pay Executive a base salary ("Base Salary") at the
annual rate of $250,000, less applicable taxes and withholdings, payable
bi-weekly in installments at such times as the Company customarily pays its
other senior level executives. Executive's Base Salary shall be reviewed
annually for appropriate increases by the Board, CEO, or compensation committee
pursuant to the normal performance review policies for senior level executives.

         1.4      Incentive Compensation. The Executive shall participate in
short-term and long-term incentive programs established by the Company for its
senior level executives generally, at levels determined by the Board or the
compensation committee. Executive's incentive compensation shall be subject to
the terms of the applicable plans and shall be determined based on Executive's
individual performance and Company performance as determined by the Board or the
compensation committee.

         1.5      Retirement and Welfare Plans. Executive shall participate in
employee retirement and welfare benefit plans made available to the Company's
senior level executives as a group or to its employees generally, as such
retirement and welfare plans may be in effect from time to time and subject to
the eligibility requirements of the plans. Nothing in this Agreement shall
prevent the Company from amending or terminating any retirement, welfare or
other employee benefit plans or programs from time to time as the Company deems
appropriate.

         1.6      Reimbursement of Expenses; Vacation. Executive may participate
in any and all benefit programs, including reimbursement of expenses and
vacation, which the Company makes available to its employees from time to time,
provided Executive is eligible under (and subject to all provisions of) the
policy and/or plan documents that govern these programs. The Company reserves
the right to change, add or cease any particular benefit without notice, in its
sole discretion, provided that these programs shall not be changed or terminated
to the detriment of the Executive unless the programs are similarly modified or
terminated with respect to all employees generally, or as otherwise required by
law. For purposes of determining vacation eligibility, Executive will be deemed
to have ten (10) years tenure with the Company.

2.       Termination. Executive's employment shall terminate upon the occurrence
of any of the following events:

         2.1      Termination Without Cause or Resignation for Good Reason
Before A Change of Control.

                  (a)      Subject to Section 2.2 below, if the Company
terminates Executive's employment without Cause (as defined in Section 2.9) at
any time before a Change of Control or Executive resigns for Good Reason (as
defined in Section 2.9) at any time before a Change of Control, this Section 2.1
shall apply.

                  (b)      If Executive's employment terminates as described in
subsection (a) above and Executive executes and does not revoke a written
separation agreement and release, in a form provided by the Company, of any and
all claims against the Company and all related parties with respect to all
matters arising out of Executive's employment by the Company, or the termination
thereof (the "Release"), Executive shall be entitled to receive the following



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severance compensation, as long as Executive complies with the terms of
Executive's Proprietary Information Agreement (as defined below):

                           (i)      Executive shall receive severance payments
in an amount equal to .5 times Executive's annual Base Salary at the rate in
effect at the time of Executive's termination. The severance amount shall be
paid in accordance with the Company's normal payroll practices over the 6-month
period following Executive's termination of employment (the "Severance Period").
Payments shall commence within 30 days after the effective date of the
termination (or the end of the revocation period for the Release, if later).

                           (ii)     During the Severance Period, Executive shall
continue to receive the medical coverage in effect at the date of Executive's
termination (or generally comparable coverage) for Executive and, where
applicable, Executive's spouse and dependents, as the same may be changed from
time to time for employees generally, as if Executive had continued in
employment during such period, or, as an alternative, the Company may elect to
pay Executive cash in lieu of such coverage in an amount equal to Executive's
COBRA cost of continuing such coverage (less any required employee payments
calculated as if Executive had continued to be an employee), where such coverage
may not be continued (or where such continuation would adversely affect the tax
status of the plan pursuant to which the coverage is provided). After the
Severance Period, the Executive shall be responsible for assuming all costs
associated with continuing medical coverage pursuant to COBRA. The COBRA health
care continuation coverage period under Section 4980B of the Internal Revenue
Code of 1986, as amended (the "Code"), shall run concurrently with the Severance
Period.

                           (iii)    Stock Options.

All outstanding stock options and stock awards held by Executive at the date of
Executive's termination of employment that would have otherwise become vested
and exercisable during the Severance Period will become vested and exercisable
during the Severance Period as if Executive had remained employed during the
Severance Period. Subject to the provisions of Section 2.2(a) below, Executive
shall have up to ninety (90) days following the expiration of the Severance
Period to exercise his vested options or awards (provided that nothing in this
Agreement shall extend the right of exercise beyond the earlier of (a) the final
exercise or termination date, as set forth in the respective option or award
agreement, or (b) the date of termination, cancellation or exchange of an option
as a result of a change in the Company's capitalization or any reorganization
event, including (i) any merger or consolidation of the Company with or into
another entity as a result of which the Common Stock of the Company is converted
into or exchanged for the right to receive cash, securities or other property or
is cancelled, (ii) any exchange of all of the Common Stock of the Company for
cash, securities or other property pursuant to a share exchange transaction,
(iii) any liquidation or dissolution of the Company, or (iv) any similar event)
All options or awards not exercised at the end of this period shall expire and
be null and void. All stock option or stock award agreements between the
Executive and the Company shall continue in full force and effect except that in
the event of any conflict between this Agreement and either the stock option or
award agreement or relevant stock plan, the terms of this Agreement shall
prevail, except that this Agreement shall not be construed to limit, in any way,
Executive's rights granted under Executive's option or award agreements or
relevant stock plan.



                                       3
<PAGE>

                           (iv)     Executive shall receive any benefits in
accordance with the terms of any applicable benefit plans and programs of the
Company accrued as of the date of the termination.

                  (c)      Executive agrees that if Executive fails to comply
with Executive's Proprietary Information Agreement, all payments under this
Section 2.1 shall immediately cease.

         2.2      Termination Without Cause; Resignation for Good Reason After
or in Connection With A Change of Control.

                  (a)      If a Change of Control occurs and (i) the Company has
terminated Executive's employment without Cause within the period of time
commencing three (3) months prior to the public announcement by the Company or
the acquiring company of such Change of Control and extending until the Change
in Control, and unless the Company can reasonably demonstrate that such
termination did not arise in connection with such Change of Control, or (ii) the
Company terminates Executive's employment without Cause at any time upon or
after a Change of Control, or (iii) Executive resigns for Good Reason (as
defined in Section 2.9) upon or at any time during the 12-month period following
the Change of Control, this Section 2.2 shall apply.

                  (b)      If Executive's employment terminates as described in
subsection (a) above and Executive executes and does not revoke a Release,
Executive shall be entitled to receive the following severance compensation, as
long as Executive complies with the terms of Executive's Proprietary Information
Agreement (as defined below):

                           (i)      Executive shall receive a lump sum severance
payment in an amount equal to (A) one times Executive's annual Base Salary at
the rate in effect at the time of Executive's termination, plus (B) one times
the greater of (X) Executive's annual bonus paid by the Company to Executive for
the fiscal year preceding Executive's termination of employment or (Y) the
Executive's target annual bonus for the then current year. The payment shall be
made within 30 days after the effective date of the termination of employment
(or the end of the revocation period for the Release, if later).

                           (ii)     During the 12-month period following
Executive's termination of employment (the "CIC Severance Period"), Executive
shall continue to receive the medical coverage in effect at the date of
Executive's termination (or generally comparable coverage) for Executive and,
where applicable, Executive's spouse and dependents, as the same may be changed
from time to time for employees generally, as if Executive had continued in
employment during such period, or, as an alternative, the Company may elect to
pay Executive cash in lieu of such coverage in an amount equal to Executive's
COBRA cost of continuing such coverage (less any required employee payments
calculated as if Executive had continued to be an employee), where such coverage
may not be continued (or where such continuation would adversely affect the tax
status of the plan pursuant to which the coverage is provided). After the CIC
Severance Period, the Executive shall be responsible for assuming all costs
associated with continuing medical coverage pursuant to COBRA. The COBRA health
care continuation coverage period under Section 4980B of the Code shall run
concurrently with the CIC Severance Period.



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<PAGE>

                           (iii)    Without limiting any acceleration of vesting
provided for under Executive's stock option or stock award agreements in
connection with a Change of Control, all outstanding stock options and stock
awards held by Executive at the date of Executive's termination of employment
shall become fully vested and exercisable on the date of termination of
employment. Executive shall have up to ninety (90) days following his date of
termination to exercise his vested options or awards. All options or awards not
exercised at the end of this period shall expire and be null and void.
Notwithstanding any other provision of this Agreement but subject to the next
succeeding sentence of this subsection (iii), if Executive's employment is
terminated pursuant to Section 2.2(a)(i) above, then Executive shall have up to
ninety (90) days following the Change of Control to exercise his vested options
and awards. Nothing in this Agreement shall extend the right of exercise beyond
the earlier of (a) the final exercise or termination date, as set forth in the
respective stock option or stock award agreements, or (b) the date of
termination, cancellation or exchange of an option as a result of a change in
the Company's capitalization or any reorganization event, including (i) any
merger or consolidation of the Company with or into another entity as a result
of which the Common Stock of the Company is converted into or exchanged for the
right to receive cash, securities or other property or is cancelled, (ii) any
exchange of all of the Common Stock of the Company for cash, securities or other
property pursuant to a share exchange transaction, (iii) any liquidation or
dissolution of the Company, or (iv) any similar event; provided that if any of
Executive's stock options or stock awards would terminate upon a Change of
Control because they are not assumed by the successor entity, all of Executive's
outstanding stock options and stock awards shall become vested immediately prior
to the Change of Control, within a timeframe determined by the Compensation
Committee of the Company, and reasonably acceptable to Executive, to allow
Executive to exercise all of his options and/or awards prior to the Change of
Control; provided that the options or awards not vested immediately prior to the
Change of Control shall be subject to the effectiveness of the Change of
Control. All stock option and stock awards agreements between the Executive and
the Company shall continue in full force and effect, except that in the event of
any conflict between this Agreement and either the stock option or award
agreement or relevant stock plan, the terms of this Agreement shall prevail,
except that this Agreement shall not be construed to limit, in any way,
Executive's rights granted under Executive's stock option or stock award
agreements or relevant stock plan.

                           (iv)     Executive shall receive any benefits accrued
in accordance with the terms of any applicable benefit plans and programs of the
Company as of the date of termination.

                  (c)      If Executive's employment is terminated pursuant to
Section 2.2(a)(i) above, then (i) subject to the provisions of Section 2.2(b),
Executive shall be entitled to receive the severance compensation set forth in
Section 2.2(b) above and the provisions of Section 2.3 below in lieu of the
severance compensation set forth in Section 2.1 above, and (ii) any amounts owed
to Executive pursuant to this Section 2.2 shall be offset by the amounts already
paid to Executive pursuant to Section 2.1. In addition, to the extent any stock
option has terminated pursuant to the provisions of Section 2.1(b)(iii) above,
such termination shall be null and void, and Executive shall have the rights
pursuant to Section 2.2(b) above (subject to the provisions of Section 2.2
(b)(iii) above).



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                  (d)      Executive agrees that if Executive materially
breaches the terms of Executive's Proprietary Information Agreement (as defined
below), all payments under this Section 2.2 shall immediately cease.

         2.3      Increase in Payments Upon a Change of Control.

                  (a)      Anything in this Agreement to the contrary
notwithstanding, in the event that it shall be determined that any payment or
distribution by the Company to or for the benefit of Executive, whether paid or
payable or distributed or distributable pursuant to the terms of this Agreement
or otherwise (a "Payment"), would constitute an "excess parachute payment"
within the meaning of Section 280G of the Code, the Company shall pay to
Executive an additional amount (the "Gross-Up Payment") such that the net amount
retained by Executive after deduction of any excise tax imposed under Section
4999 of the Code, and any federal, state and local income tax, employment tax
and excise tax imposed upon the Gross-Up Payment, shall be equal to the Payment.
For purposes of determining the amount of the Gross-Up Payment, unless Executive
specifies that other rates apply, Executive shall be deemed to pay federal
income tax and employment taxes at the highest marginal rate of federal income
and employment taxation in the calendar year in which the Gross-Up Payment is to
be made and state and local income taxes at the highest marginal rate of
taxation in the state and locality of Executive's residence on Executive's
termination date, net of the maximum reduction in federal income taxes that may
be obtained from the deduction of such state and local taxes.

                  (b)      All determinations to be made under this Section 2.3
shall be made by the Company's independent public accountant immediately prior
to the Change of Control or by another independent public accounting firm
mutually selected by the Company and Executive before the date of the Change of
Control (the "Accounting Firm"), which firm shall provide its determinations and
any supporting calculations both to the Company and Executive within 20 days
after Executive's termination date. Any such determination by the Accounting
Firm shall be binding upon the Company and Executive. Within 10 days after the
Accounting Firm's determination, the Company shall pay the Gross-Up Payment to
Executive.

                  (c)      All of the fees and expenses of the Accounting Firm
in performing the determinations referred to in this Section 2.3 shall be borne
solely by the Company.

         2.4      Voluntary Termination. Executive may voluntarily terminate
Executive's employment for any reason upon 30 days' prior written notice. In
such event, after the effective date of such termination, except as provided in
Sections 2.1 and 2.2 with respect to a resignation for Good Reason, no further
payments shall be due under this Agreement, except that Executive shall be
entitled to any benefits accrued as of the employment termination date in
accordance with the terms of any applicable benefit plans and programs of the
Company.

         2.5      Disability. The Company may terminate Executive's employment
if Executive has been unable to perform the material duties of Executive's
employment for a period of 90 days (which need not be consecutive) in any
12-month period because of physical or mental injury or illness ("Disability");
provided, however, that the Company shall continue to pay Executive's Base
Salary until the Company acts to terminate Executive's employment. Executive
agrees, in the event of a dispute under this Section 2.5 relating to Executive's



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Disability, to submit to a physical examination by a licensed physician jointly
selected by the Board and Executive. If the Company terminates Executive's
employment for Disability, no further payments shall be due under this
Agreement, except that Executive shall be entitled to any benefits accrued as of
the employment termination date in accordance with the terms of any applicable
benefit plans and programs of the Company.

         2.6      Death. If Executive dies while employed by the Company, the
Company shall pay to Executive's executor, legal representative, administrator
or designated beneficiary, as applicable, any benefits accrued as of the date of
death under the Company's benefit plans and programs. Otherwise, the Company
shall have no further liability or obligation under this Agreement to
Executive's executors, legal representatives, administrators, heirs or assigns
or any other person claiming under or through Executive.

         2.7      Cause. The Company may terminate Executive's employment at any
time for Cause (as defined in Section 2.9) upon written notice to Executive, in
which event all payments under this Agreement shall cease. Executive shall be
entitled to any benefits accrued before Executive's termination in accordance
with the terms of any applicable benefit plans and programs of the Company.

         2.8      Notice of Termination. Any termination of Executive's
employment shall be communicated by a written notice of termination to the other
party hereto given in accordance with Section 7. The notice of termination shall
(i) indicate the specific termination provision in this Agreement relied upon,
(ii) briefly summarize the facts and circumstances deemed to provide a basis for
a termination of employment and the applicable provision hereof, and (iii)
specify the termination date in accordance with the requirements of this
Agreement.

         2.9      Definitions.

                  (a)      "Cause" shall mean any of the following grounds for
termination of Executive's employment:

                           (i)      Executive shall have been convicted of,
indicted for, or entered a plea of guilty or nolo contendere to, any crime
involving moral turpitude or any felony;

                           (ii)     Executive intentionally and continually
fails to perform Executive's reasonably assigned material duties to the Company
(other than a failure resulting from Executive's incapacity due to physical or
mental illness), which failure has continued for a period of at least 30 days
after a written notice of demand for substantial performance, signed by a duly
authorized officer of the Company, has been delivered to Executive specifying
the manner in which Executive has failed substantially to perform; or

                           (iii)    Executive materially breaches the terms of
Executive's Proprietary Information Agreement.

                  (b)      "Change of Control" as used herein, a "Change of
Control" shall be deemed to have occurred if:



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                           (i)      Any "person" (as such term is used in
sections 13(d) and 14(d) of the Securities Exchange Act of 1934, as amended (the
"Exchange Act")) becomes a "beneficial owner" (as defined in Rule 13d-3 under
the Exchange Act), directly or indirectly, of securities of the Company
representing more than 50% of the voting power of the then outstanding
securities of the Company; provided that a Change of Control shall not be deemed
to occur as a result of a transaction in which the Company becomes a subsidiary
of another corporation and in which the stockholders of the Company, immediately
prior to the transaction, will beneficially own, immediately after the
transaction, shares entitling such stockholders to more than 50% of all votes to
which all stockholders of the parent corporation would be entitled in the
election of directors; or

                           (ii)     The consummation of (A) a merger or
consolidation of the Company with another corporation where the stockholders of
the Company, immediately prior to the merger or consolidation, will not
beneficially own, immediately after the merger or consolidation, shares
entitling such stockholders to more than 50% of all votes to which all
stockholders of the surviving corporation would be entitled in the election of
directors, (B) a sale or other disposition of all or substantially all of the
assets of the Company, or (C) a liquidation or dissolution of the Company.

                  (c)      "Good Reason" shall mean the occurrence of any of the
following events or conditions, unless Executive has expressly consented in
writing thereto, or except as a result of Executive's physical or mental
incapacity or as described in the last sentence of this subsection (c):

                           (i)      a reduction in Executive's Base Salary or
target Bonus prior to a Change of Control (as defined above) whereby Executive's
Base Salary or target Bonus are decreased by more than 10% from Executive's
immediately preceding Base Salary or target Bonus amount; provided however, that
such reduction shall not trigger Good Reason if all similarly situated
executives are similarly affected by a decrease in Base Salary or target Bonus;
provided further, if such decreases are equal to or greater than 20% of
Executive's Base Salary or target Bonus, Good Reason shall be available to the
Executive;

                           (ii)     a reduction in Executive's Base Salary or
target Bonus after a Change of Control (as defined above);

                           (iii)    a substantial reduction of Executive's
duties and responsibilities hereunder or diminution of title; or

                           (iv)     the Company requires that Executive's
principal office location be moved to a location more than 50 miles from
Executive's principal office location or principal residence (as defined by
Section 217 of the Code) immediately before the change in location (provided
that Executive, at the time of termination of employment, does not have a
principal residence (as defined by Section 217 of the Code) 50 miles from the
Executive's principal office).



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Notwithstanding the foregoing, Executive shall not have Good Reason for
termination unless Executive gives written notice of termination for Good Reason
within 30 days after the event giving rise to Good Reason occurs and the Company
does not correct the action or failure to act that constitutes the grounds for
Good Reason, as set forth in Executive's notice of termination, within 30 days
after the date on which Executive gives written notice of termination.

3.       Non-Exclusivity of Rights. Nothing in this Agreement shall prevent or
limit Executive's continuing or future participation in or rights under any
benefit, bonus, incentive or other plan or program provided by the Company and
for which Executive may qualify; provided, however, that if Executive becomes
entitled to and receives the payments provided for in Section 2 of this
Agreement, Executive hereby waives Executive's right to receive payments under
any severance plan or similar program applicable to all employees of the
Company.

4.       Employee Proprietary Information, Inventions and Noncompete Agreement.
Executive hereby acknowledges his obligations pursuant to his Employee
Proprietary Information, Inventions and Noncompete Agreement attached hereto as
Exhibit A (the "Proprietary Information Agreement"), including but not limited
to, the obligation to refrain from using or disclosing the proprietary
information of the Company. Executive acknowledges that these obligations shall
survive the termination of his employment with the Company, consistent with the
terms of the Proprietary Information Agreement.

5.       Survivorship. The respective rights and obligations of the parties
under this Agreement shall survive any termination of Executive's employment to
the extent necessary to the intended preservation of such rights and
obligations.

6.       Mitigation. Executive shall not be required to mitigate the amount of
any payment or benefit provided for in this Agreement by seeking other
employment or otherwise and there shall be no offset against amounts due
Executive under this Agreement on account of any remuneration attributable to
any subsequent employment that Executive may obtain.

7.       Notices. All notices and other communications required or permitted
under this Agreement or necessary or convenient in connection herewith shall be
in writing and shall be deemed to have been given when hand delivered or mailed
by registered or certified mail, as follows (provided that notice of change of
address shall be deemed given only when received):

         If to the Company, to:

         NxStage Medical, Inc.
         439 South Union Street, 5th Floor
         Lawrence, MA  01843
         ATTN: Chief Executive Officer with copy to General Counsel

         If to Executive, to:

         Robert S. Brown
         6 Tennyson Road
         Wellesley, Massachusetts 02481






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or to such other names or addresses as the Company or Executive, as the case may
be, shall designate by notice to each other person entitled to receive notices
in the manner specified in this Section.

8.       Contents of Agreement; Amendment and Assignment.

                  (a)      This Agreement, together with the Proprietary
Information Agreement, sets forth the entire understanding between the parties
hereto with respect to the subject matter hereof and supercedes any and all
prior agreements and understandings concerning Executive's employment by the
Company, and cannot be changed, modified, extended or terminated except upon
written amendment approved by the Board and executed on its behalf by a duly
authorized officer of the Company and by Executive.

                  (b)      All of the terms and provisions of this Agreement
shall be binding upon and inure to the benefit of and be enforceable by the
respective heirs, executors, administrators, legal representatives, successors
and assigns of the parties hereto, except that the duties and responsibilities
of Executive under this Agreement are of a personal nature and shall not be
assignable or delegatable in whole or in part by Executive. The Company shall
require any successor (whether direct or indirect, by purchase, merger,
consolidation, reorganization or otherwise) to all or substantially all of the
business or assets of the Company, within 15 days of such succession, expressly
to assume and agree to perform this Agreement in the same manner and to the same
extent as the Company would be required to perform if no such succession had
taken place.

9.       Severability. If any provision of this Agreement or application thereof
to anyone or under any circumstances is adjudicated to be invalid or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect any other provision or application of this Agreement which can be given
effect without the invalid or unenforceable provision or application and shall
not invalidate or render unenforceable such provision or application in any
other jurisdiction. If any provision is held void, invalid or unenforceable with
respect to particular circumstances, it shall nevertheless remain in full force
and effect in all other circumstances.

10.      Remedies Cumulative; No Waiver. No remedy conferred upon a party by
this Agreement is intended to be exclusive of any other remedy, and each and
every such remedy shall be cumulative and shall be in addition to any other
remedy given under this Agreement or now or hereafter existing at law or in
equity. No delay or omission by a party in exercising any right, remedy or power
under this Agreement or existing at law or in equity shall be construed as a
waiver thereof, and any such right, remedy or power may be exercised by such
party from time to time and as often as may be deemed expedient or necessary by
such party in its sole discretion.


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<PAGE>




11.      Withholding; Taxation. All payments under this Agreement shall be made
subject to applicable tax withholding, and the Company shall withhold from any
payments under this Agreement all federal, state and local taxes as the Company
is required to withhold pursuant to any law or governmental rule or regulation.
Except as otherwise provided by Section 2.3, Executive shall bear all expense
of, and be solely responsible for, all federal, state and local taxes due with
respect to any payment received under this Agreement.

         The parties intend that all payments hereunder shall comply with
Section 409A of the Code. Executive agrees that the Company may revise the
timing or nature of payments in this Agreement to the extent necessary to comply
with Section 409A (although the parties agree that the provisions of this
Agreement are not intended to be deferred compensation subject to such section).

12.      Miscellaneous. This Agreement may be executed in counterparts, each of
which is an original. It shall not be necessary in making proof of this
Agreement or any counterpart hereof to produce or account for any of the other
counterparts.

13.      Governing Law. This Agreement shall be governed by and interpreted
under the laws of the Commonwealth of Massachusetts without giving effect to any
conflict of laws provisions or canons of construction that construe agreements
against the draftsperson.




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<PAGE>



         IN WITNESS WHEREOF, the undersigned, intending to be legally bound,
have executed this Agreement as of the date first above written.


                                             NxSTAGE MEDICAL, INC.


                                             By: /s/ Jeffrey H. Burbank
                                                 -------------------------------
                                             Name: Jeffrey H. Burbank
                                             Title: President & CEO


                                             EXECUTIVE


                                             /s/ Robert S. Brown
                                             -----------------------------------

                                             Name: Robert S. Brown



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