Document:

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                                                                   Exhibit 10.22

                              NXSTAGE MEDICAL, INC.

                            2005 STOCK INCENTIVE PLAN

1.   Purpose

     The purpose of this 2005 Stock Incentive Plan (the "Plan") of NxStage
Medical, Inc., a Delaware corporation (the "Company"), is to advance the
interests of the Company's stockholders by enhancing the Company's ability to
attract, retain and motivate persons who are expected to make important
contributions to the Company and by providing such persons with equity ownership
opportunities and performance-based incentives that are intended to align their
interests with those of the Company's stockholders. Except where the context
otherwise requires, the term "Company" shall include any of the Company's
present or future parent or subsidiary corporations as defined in Sections
424(e) or (f) of the Internal Revenue Code of 1986, as amended, and any
regulations promulgated thereunder (the "Code") and any other business venture
(including, without limitation, joint venture or limited liability company) in
which the Company has a controlling interest, as determined by the Board of
Directors of the Company (the "Board").

2.   Eligibility

     All of the Company's employees, officers, directors, consultants and
advisors are eligible to receive options, stock appreciation rights, restricted
stock, restricted stock units and other stock-based awards (each, an "Award")
under the Plan. Each person who receives an Award under the Plan is deemed a
"Participant."

3.   Administration and Delegation

     (a) Administration by Board of Directors. The Plan will be administered by
the Board. The Board shall have authority to grant Awards and to adopt, amend
and repeal such administrative rules, guidelines and practices relating to the
Plan as it shall deem advisable. The Board may correct any defect, supply any
omission or reconcile any inconsistency in the Plan or any Award in the manner
and to the extent it shall deem expedient to carry the Plan into effect and it
shall be the sole and final judge of such expediency. All decisions by the Board
shall be made in the Board's sole discretion and shall be final and binding on
all persons having or claiming any interest in the Plan or in any Award. No
director or person acting pursuant to the authority delegated by the Board shall
be liable for any action or determination relating to or under the Plan made in
good faith.

     (b) Appointment of Committees. To the extent permitted by applicable law,
the Board may delegate any or all of its powers under the Plan to one or more
committees or subcommittees of the Board (a "Committee"). All references in the
Plan to the "Board" shall mean the Board or a Committee of the Board to the
extent that the Board's powers or authority under the Plan have been delegated
to such Committee.
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4.   Stock Available for Awards

     (a) Number of Shares. Subject to adjustment under Section 9, Awards may be
made under the Plan for up to the number of shares of common stock, $0.001 par
value per share, of the Company (the "Common Stock") that is equal to the sum
of:

          (1) such number of shares of Common Stock as is equal to the sum of
(x) the number of shares of Common Stock reserved for issuance under the
Company's 1999 Stock Option and Grant Plan (the "Existing Plan") that remain
available for grant under the Existing Plan immediately prior to the closing of
the Company's initial public offering and (y) the number of shares of Common
Stock subject to awards granted under the Existing Plan which awards expire,
terminate or are otherwise surrendered, canceled, forfeited or repurchased by
the Company at their original issuance price pursuant to a contractual
repurchase right (subject, however, in the case of Incentive Stock Options (as
hereinafter defined) to any limitations of the Code); plus

          (2) an annual increase to be added on the first day of each of the
Company's fiscal years during the period beginning in fiscal year 2007 and
ending on the second day of fiscal year 2015 equal to the lesser of (i) 600,000
shares of Common Stock, (ii) 3% of the outstanding shares on such date or
(ii) an amount determined by the Board.

     Notwithstanding clause (2) above, in no event shall the number of shares
available under this Plan be increased as set forth in clause (2) to the extent
such increase, in addition to any other increases proposed by the Board in the
number of shares available for issuance under all other employee or director
stock plans, would result in the total number of shares then available for
issuance under all employee and director stock plans exceeding 30% of the
outstanding shares of the Company on the first day of the applicable fiscal
year.

     If any Award expires or is terminated, surrendered or canceled without
having been fully exercised or is forfeited in whole or in part (including as
the result of shares of Common Stock subject to such Award being repurchased by
the Company at the original issuance price pursuant to a contractual repurchase
right) or results in any Common Stock not being issued, the unused Common Stock
covered by such Award shall again be available for the grant of Awards under the
Plan. Further, shares of Common Stock tendered to the Company by a Participant
to exercise an Award shall be added to the number of shares of Common Stock
available for the grant of Awards under the Plan. However, in the case of
Incentive Stock Options (as hereinafter defined), the foregoing provisions shall
be subject to any limitations under the Code. Shares issued under the Plan may
consist in whole or in part of authorized but unissued shares or treasury
shares.

     (b) Per-Participant Limit. Subject to adjustment under Section 9, for
Awards granted after the Common Stock is registered under the Securities
Exchange Act of 1934 (the "Exchange Act"), the maximum number of shares of
Common Stock with respect to which Awards may be
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granted to any Participant under the Plan shall be 1,000,000(1) per calendar
year. For purposes of the foregoing limit, the combination of an Option in
tandem with an SAR (as each is hereafter defined) shall be treated as a single
Award. The per-Participant limit described in this Section 4(b) shall be
construed and applied consistently with Section 162(m) of the Code or any
successor provision thereto, and the regulations thereunder ("Section 162(m)").

5.   Stock Options

     (a) General. The Board may grant options to purchase Common Stock (each, an
"Option") and determine the number of shares of Common Stock to be covered by
each Option, the exercise price of each Option and the conditions and
limitations applicable to the exercise of each Option, including conditions
relating to applicable federal or state securities laws, as it considers
necessary or advisable. An Option which is not intended to be an Incentive Stock
Option (as hereinafter defined) shall be designated a "Nonstatutory Stock
Option."

     (b) Incentive Stock Options. An Option that the Board intends to be an
"incentive stock option" as defined in Section 422 of the Code (an "Incentive
Stock Option") shall only be granted to employees of NxStage, any of NxStage's
present or future parent or subsidiary corporations as defined in Sections
424(e) or (f) of the Code, and any other entities the employees of which are
eligible to receive Incentive Stock Options under the Code, and shall be subject
to and shall be construed consistently with the requirements of Section 422 of
the Code. The Company shall have no liability to a Participant, or any other
party, if an Option (or any part thereof) that is intended to be an Incentive
Stock Option is not an Incentive Stock Option or for any action taken by the
Board pursuant to Section 10(f), including without limitation the conversion of
an Incentive Stock Option to a Nonstatutory Stock Option.

     (c) Exercise Price. The Board shall establish the exercise price of each
Option and specify such exercise price in the applicable option agreement.

     (d) Duration of Options. Each Option shall be exercisable at such times and
subject to such terms and conditions as the Board may specify in the applicable
option agreement.

     (e) Exercise of Option. Options may be exercised by delivery to the Company
of a written notice of exercise signed by the proper person or by any other form
of notice (including electronic notice) approved by the Board together with
payment in full as specified in Section 5(f) for the number of shares for which
the Option is exercised. Shares of Common Stock subject to the Option will be
delivered by the Company following exercise either as soon as practicable or,
subject to such conditions as the Board shall specify, on a deferred basis (with
the Company's obligation to be evidenced by an instrument providing for future
delivery of the deferred shares at the time or times specified by the Board).

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(1)  After giving effect to the proposed reverse stock split of the Company's
     Common Stock in anticipation of the initial public offering.

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     (f) Payment Upon Exercise. Common Stock purchased upon the exercise of an
Option granted under the Plan shall be paid for as follows:

          (1) in cash or by check, payable to the order of the Company;

          (2) except as the Board may otherwise provide in an option agreement,
by (i) delivery of an irrevocable and unconditional undertaking by a
creditworthy broker to deliver promptly to the Company sufficient funds to pay
the exercise price and any required tax withholding or (ii) delivery by the
Participant to the Company of a copy of irrevocable and unconditional
instructions to a creditworthy broker to deliver promptly to the Company cash or
a check sufficient to pay the exercise price and any required tax withholding;

          (3) when the Common Stock is registered under the Exchange Act, by
delivery of shares of Common Stock owned by the Participant valued at their fair
market value as determined by (or in a manner approved by) the Board ("Fair
Market Value"), provided (i) such method of payment is then permitted under
applicable law, (ii) such Common Stock, if acquired directly from the Company,
was owned by the Participant for such minimum period of time, if any, as may be
established by the Board in its discretion and (iii) such Common Stock is not
subject to any repurchase, forfeiture, unfulfilled vesting or other similar
requirements;

          (4) to the extent permitted by applicable law and by the Board, by (i)
delivery of a promissory note of the Participant to the Company on terms
determined by the Board, or (ii) payment of such other lawful consideration as
the Board may determine; or

          (5) by any combination of the above permitted forms of payment.

     (g) Substitute Options. In connection with a merger or consolidation of an
entity with the Company or the acquisition by the Company of property or stock
of an entity, the Board may grant Options in substitution for any options or
other stock or stock-based awards granted by such entity or an affiliate
thereof. Substitute Options may be granted on such terms as the Board deems
appropriate in the circumstances, notwithstanding any limitations on Options
contained in the other sections of this Section 5 or in Section 2. Substitute
Options shall not count against the overall share limit set forth in Section
4(a), except as may be required by reason of Section 422 and related provisions
of the Code.

6.   Stock Appreciation Rights

     (a) General. A Stock Appreciation Right, or SAR, is an Award entitling the
holder, upon exercise, to receive an amount of Common Stock determined by
reference to appreciation, from and after the date of grant, in the fair market
value of a share of Common Stock. The date as of which such appreciation or
other measure is determined shall be the exercise date.

     (b) Grants. Stock Appreciation Rights may be granted in tandem with, or
independently of, Options granted under the Plan.

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          (1) Rules Applicable to Tandem Awards. When Stock Appreciation Rights
are expressly granted in tandem with Options, (i) the Stock Appreciation Right
will be exercisable only at such time or times, and to the extent, that the
related Option is exercisable (except to the extent designated by the Board in
connection with a Reorganization Event or a Change in Control Event) and will be
exercisable in accordance with the procedure required for exercise of the
related Option; (ii) the Stock Appreciation Right will terminate and no longer
be exercisable upon the termination or exercise of the related Option, except to
the extent designated by the Board in connection with a Reorganization Event or
a Change in Control Event and except that a Stock Appreciation Right granted
with respect to less than the full number of shares covered by an Option will
not be reduced until the number of shares as to which the related Option has
been exercised or has terminated exceeds the number of shares not covered by the
Stock Appreciation Right; (iii) the Option will terminate and no longer be
exercisable upon the exercise of the related Stock Appreciation Right; and (iv)
the Stock Appreciation Right will be transferable only with the related Option.

          (2) Exercise of Independent SARs. A Stock Appreciation Right not
expressly granted in tandem with an Option will become exercisable at such time
or times, and on such conditions, as the Board may specify in the SAR Award.

     (c) Exercise. Stock Appreciation Rights may be exercised by delivery to the
Company of a written notice of exercise signed by the proper person or by any
other form of notice (including electronic notice) approved by the Board,
together with any other documents required by the Board.

7.   Restricted Stock; Restricted Stock Units

     (a) General. The Board may grant Awards entitling recipients to acquire
shares of Common Stock ("Restricted Stock"), subject to the right of the Company
to repurchase all or part of such shares at their issue price or other stated or
formula price (or to require forfeiture of such shares if issued at no cost)
from the recipient in the event that conditions specified by the Board in the
applicable Award are not satisfied prior to the end of the applicable
restriction period or periods established by the Board for such Award. Instead
of granting Awards for Restricted Stock, the Board may grant Awards entitling
the recipient to receive shares of Common Stock to be delivered at the time such
shares of Common Stock vest ("Restricted Stock Units") (Restricted Stock and
Restricted Stock Units are each referred to herein as a "Restricted Stock
Award").

     (b) Terms and Conditions. The Board shall determine the terms and
conditions of a Restricted Stock Award, including the conditions for repurchase
(or forfeiture) and the issue price, if any.

     (c) Stock Certificates. Any stock certificates issued in respect of a
Restricted Stock Award shall be registered in the name of the Participant and,
unless otherwise determined by the Board, deposited by the Participant, together
with a stock power endorsed in blank, with the Company (or its designee). At the
expiration of the applicable restriction periods, the Company

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(or such designee) shall deliver the certificates no longer subject to such
restrictions to the Participant or if the Participant has died, to the
beneficiary designated, in a manner determined by the Board, by a Participant to
receive amounts due or exercise rights of the Participant in the event of the
Participant's death (the "Designated Beneficiary"). In the absence of an
effective designation by a Participant, "Designated Beneficiary" shall mean the
Participant's estate.

8.   Other Stock-Based Awards

     Other Awards of shares of Common Stock, and other Awards that are valued in
whole or in part by reference to, or are otherwise based on, shares of Common
Stock or other property, may be granted hereunder to Participants ("Other Stock
Unit Awards"), including without limitation Awards entitling recipients to
receive shares of Common Stock to be delivered in the future. Such Other Stock
Unit Awards shall also be available as a form of payment in the settlement of
other Awards granted under the Plan or as payment in lieu of compensation to
which a Participant is otherwise entitled. Other Stock Unit Awards may be paid
in shares of Common Stock or cash, as the Board shall determine. Subject to the
provisions of the Plan, the Board shall determine the conditions of each Other
Stock Unit Award, including any purchase price applicable thereto.

9.   Adjustments for Changes in Common Stock and Certain Other Events

     (a) Changes in Capitalization. In the event of any stock split, reverse
stock split, stock dividend, recapitalization, combination of shares,
reclassification of shares, spin-off or other similar change in capitalization
or event, or any distribution to holders of Common Stock other than an ordinary
cash dividend, (i) the number and class of securities available under this Plan,
(ii) the per-Participant limit set forth in Section 4(b), (iii) the number and
class of securities and exercise price per share of each outstanding Option,
(iv) the share- and per-share provisions of each Stock Appreciation Right, (v)
the repurchase price per share subject to each outstanding Restricted Stock
Award, and (vi) the share- and per-share-related provisions of each outstanding
Other Stock Unit Award, shall be appropriately adjusted by the Company (or
substituted Awards may be made, if applicable) to the extent determined by the
Board.

     (b) Reorganization and Change in Control Events

          (1)  Definitions

               (a)  A "Reorganization Event" shall mean:

                    (i)  any merger or consolidation of the Company with or into
                         another entity as a result of which all of the Common
                         Stock of the Company is converted into or exchanged for
                         the right to receive cash, securities or other property
                         or is cancelled;

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                    (ii) any exchange of all of the Common Stock of the Company
                         for cash, securities or other property pursuant to a
                         share exchange transaction; or

                    (iii) any liquidation or dissolution of the Company.

               (b)  A "Change in Control Event" shall mean:

                    (i)  the acquisition by an individual, entity or group
                         (within the meaning of Section 13(d)(3) or 14(d)(2) of
                         the Exchange Act) (a "Person") of beneficial ownership
                         of any capital stock of the Company if, after such
                         acquisition, such Person beneficially owns (within the
                         meaning of Rule 13d-3 promulgated under the Exchange
                         Act) 50% or more of either (x) the then-outstanding
                         shares of common stock of the Company (the "Outstanding
                         Company Common Stock") or (y) the combined voting power
                         of the then-outstanding securities of the Company
                         entitled to vote generally in the election of directors
                         (the "Outstanding Company Voting Securities");
                         provided, however, that for purposes of this subsection
                         (i), the following acquisitions shall not constitute a
                         Change in Control Event: (A) any acquisition directly
                         from the Company or (B) any acquisition by any
                         corporation pursuant to a Business Combination (as
                         defined below) which complies with clauses (x) and (y)
                         of subsection (iii) of this definition; or

                    (ii) such time as the Continuing Directors (as defined
                         below) do not constitute a majority of the Board (or,
                         if applicable, the Board of Directors of a successor
                         corporation to the Company), where the term "Continuing
                         Director" means at any date a member of the Board (x)
                         who was a member of the Board on the date of the
                         initial adoption of this Plan by the Board or (y) who
                         was nominated or elected subsequent to such date by at
                         least a majority of the directors who were Continuing
                         Directors at the time of such nomination or election or
                         whose election to the Board was recommended or endorsed
                         by at least a majority of the directors who were
                         Continuing Directors at the time of such nomination or
                         election; provided, however, that there shall be
                         excluded from this clause (y) any individual whose
                         initial assumption of office occurred as a result of an
                         actual or threatened election contest with respect to
                         the election or removal of directors or other actual or
                         threatened solicitation of proxies

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                         or consents, by or on behalf of a person other than the
                         Board; or

                    (iii) the consummation of a merger, consolidation,
                         reorganization, recapitalization or share exchange
                         involving the Company or a sale or other disposition of
                         all or substantially all of the assets of the Company
                         (a "Business Combination"), unless, immediately
                         following such Business Combination, each of the
                         following two conditions is satisfied: (x) all or
                         substantially all of the individuals and entities who
                         were the beneficial owners of the Outstanding Company
                         Common Stock and Outstanding Company Voting Securities
                         immediately prior to such Business Combination
                         beneficially own, directly or indirectly, more than 50%
                         of the then-outstanding shares of common stock and the
                         combined voting power of the then-outstanding
                         securities entitled to vote generally in the election
                         of directors, respectively, of the resulting or
                         acquiring corporation in such Business Combination
                         (which shall include, without limitation, a corporation
                         which as a result of such transaction owns the Company
                         or substantially all of the Company's assets either
                         directly or through one or more subsidiaries) (such
                         resulting or acquiring corporation is referred to
                         herein as the "Acquiring Corporation") in substantially
                         the same proportions as their ownership of the
                         Outstanding Company Common Stock and Outstanding
                         Company Voting Securities, respectively, immediately
                         prior to such Business Combination and (y) no Person
                         (excluding any employee benefit plan (or related trust)
                         maintained or sponsored by the Company or by the
                         Acquiring Corporation) beneficially owns, directly or
                         indirectly, 50% or more of the then-outstanding shares
                         of common stock of the Acquiring Corporation, or of the
                         combined voting power of the then-outstanding
                         securities of such corporation entitled to vote
                         generally in the election of directors (except to the
                         extent that such ownership existed prior to the
                         Business Combination); or

                    (iv) the liquidation or dissolution of the Company.

               (c)  "Good Reason" shall mean any significant diminution in the
                    Participant's title, authority, or responsibilities from and
                    after such Reorganization Event or Change in Control Event,
                    as the case may be, or any reduction in the annual cash
                    compensation payable to

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                    the Participant from and after such Reorganization Event or
                    Change in Control Event, as the case may be, or the
                    relocation of the place of business at which the Participant
                    is principally located to a location that is greater than 50
                    miles from its location immediately prior to such
                    Reorganization Event or Change in Control Event.

               (d)  "Cause" shall mean any (i) willful failure by the
                    Participant, which failure is not cured within 30 days of
                    written notice to the Participant from the Company, to
                    perform his or her material responsibilities to the Company
                    or (ii) willful misconduct by the Participant which affects
                    the business reputation of the Company. The Participant
                    shall be considered to have been discharged for "Cause" if
                    the Company determines, within 30 days after the
                    Participant's resignation, that discharge for Cause was
                    warranted.

          (2)  Effect on Options

               (a)  Reorganization Event. Upon the occurrence of a
                    Reorganization Event (regardless of whether such event also
                    constitutes a Change in Control Event), or the execution by
                    the Company of any agreement with respect to a
                    Reorganization Event (regardless of whether such event will
                    result in a Change in Control Event), the Board shall
                    provide that all outstanding Options shall be assumed, or
                    equivalent options shall be substituted, by the acquiring or
                    succeeding corporation (or an affiliate thereof); provided
                    that if such Reorganization Event also constitutes a Change
                    in Control Event, except to the extent specifically provided
                    to the contrary in the instrument evidencing any Option or
                    any other agreement between a Participant and the Company
                    (A) one-half of the number of shares subject to the Option
                    which were not already vested shall be exercisable upon the
                    occurrence of such Reorganization Event and, subject to (B)
                    below, the remaining one-half of such number of shares shall
                    continue to become vested in accordance with the original
                    vesting schedule set forth in such option, with one-half of
                    the number of shares that would otherwise have become vested
                    on each subsequent vesting date in accordance with the
                    original schedule becoming vested on each subsequent vesting
                    date and (B) such assumed or substituted options shall
                    become immediately exercisable in full if, on or prior to
                    the first anniversary of the date of the consummation of the
                    Reorganization Event, the Participant's employment with the
                    Company or the acquiring or succeeding corporation is
                    terminated for Good Reason by the Participant or is
                    terminated without Cause by the Company or the acquiring or

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                    succeeding corporation. For purposes hereof, an Option shall
                    be considered to be assumed if, following consummation of
                    the Reorganization Event, the Option confers the right to
                    purchase, for each share of Common Stock subject to the
                    Option immediately prior to the consummation of the
                    Reorganization Event, the consideration (whether cash,
                    securities or other property) received as a result of the
                    Reorganization Event by holders of Common Stock for each
                    share of Common Stock held immediately prior to the
                    consummation of the Reorganization Event (and if holders
                    were offered a choice of consideration, the type of
                    consideration chosen by the holders of a majority of the
                    outstanding shares of Common Stock); provided, however, that
                    if the consideration received as a result of the
                    Reorganization Event is not solely common stock of the
                    acquiring or succeeding corporation (or an affiliate
                    thereof), the Company may, with the consent of the acquiring
                    or succeeding corporation, provide for the consideration to
                    be received upon the exercise of Options to consist solely
                    of common stock of the acquiring or succeeding corporation
                    (or an affiliate thereof) equivalent in value (as determined
                    by the Board) to the per share consideration received by
                    holders of outstanding shares of Common Stock as a result of
                    the Reorganization Event.

                         Notwithstanding the foregoing, if the acquiring or
                    succeeding corporation (or an affiliate thereof) does not
                    agree to assume, or substitute for, such Options, or in the
                    event of a liquidation or dissolution of the Company, the
                    Board shall, upon written notice to the Participants,
                    provide that all then unexercised Options will become
                    exercisable in full as of a specified time prior to the
                    Reorganization Event and will terminate immediately prior to
                    the consummation of such Reorganization Event, except to the
                    extent exercised by the Participants before the consummation
                    of such Reorganization Event; provided, however, that in the
                    event of a Reorganization Event under the terms of which
                    holders of Common Stock will receive upon consummation
                    thereof a cash payment for each share of Common Stock
                    surrendered pursuant to such Reorganization Event (the
                    "Acquisition Price"), then the Board may instead provide
                    that all outstanding Options shall terminate upon
                    consummation of such Reorganization Event and that each
                    Participant shall receive, in exchange therefor, a cash
                    payment equal to the amount (if any) by which (A) the
                    Acquisition Price multiplied by the number of shares of
                    Common Stock subject to such outstanding Options (whether or
                    not then exercisable), exceeds (B) the aggregate exercise
                    price of such Options.

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               (b)  Change in Control Event that is not a Reorganization Event.
                    Upon the occurrence of a Change in Control Event that does
                    not also constitute a Reorganization Event, except to the
                    extent specifically provided to the contrary in the
                    instrument evidencing any Option or any other agreement
                    between a Participant and the Company, the vesting schedule
                    of such Option shall be accelerated in part so that one-half
                    of the number of shares that would otherwise have first
                    become vested on any date after the date of the Change in
                    Control Event shall immediately become exercisable. The
                    remaining one-half of such number of shares shall continue
                    to become vested in accordance with the original vesting
                    schedule set forth in such Option, with one-half of the
                    number of shares that would otherwise have become vested on
                    each subsequent vesting date in accordance with the original
                    schedule becoming vested on each such subsequent vesting
                    date; provided, however, that each such Option shall be
                    immediately exercisable in full if, on or prior to the first
                    anniversary of the date of the consummation of the Change in
                    Control Event, the Participant's employment with the Company
                    or the acquiring or succeeding corporation is terminated for
                    Good Reason by the Participant or is terminated without
                    Cause by the Company or the acquiring or succeeding
                    corporation.

          (3)  Effect on Restricted Stock Awards

               (a)  Reorganization Event that is not a Change in Control Event.
                    Upon the occurrence of a Reorganization Event that is not a
                    Change in Control Event, the repurchase and other rights of
                    the Company under each outstanding Restricted Stock Award
                    shall inure to the benefit of the Company's successor and
                    shall apply to the cash, securities or other property which
                    the Common Stock was converted into or exchanged for
                    pursuant to such Reorganization Event in the same manner and
                    to the same extent as they applied to the Common Stock
                    subject to such Restricted Stock Award.

               (b)  Change in Control Event. Upon the occurrence of a Change in
                    Control Event (regardless of whether such event also
                    constitutes a Reorganization Event), except to the extent
                    specifically provided to the contrary in the instrument
                    evidencing any Restricted Stock Award or any other agreement
                    between a Participant and the Company, the vesting schedule
                    of all Restricted Stock Awards shall be accelerated in part
                    so that one-half of the number of shares that would
                    otherwise have first become free from conditions or
                    restrictions on any date after the date of the Change in
                    Control Event shall immediately become free from conditions
                    or restrictions. Subject to the following sentence, the
                    remaining one-

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                    half of such number of shares shall continue to become free
                    from conditions or restrictions in accordance with the
                    original schedule set forth in such Restricted Stock Award,
                    with one-half of the number of shares that would otherwise
                    have become free from conditions or restrictions on each
                    subsequent vesting date in accordance with the original
                    schedule becoming free from conditions or restrictions on
                    each subsequent vesting date. In addition, each such
                    Restricted Stock Award shall immediately become free from
                    all conditions or restrictions if, on or prior to the first
                    anniversary of the date of the consummation of the Change in
                    Control Event, the Participant's employment with the Company
                    or the acquiring or succeeding corporation is terminated for
                    Good Reason by the Participant or is terminated without
                    Cause by the Company or the acquiring or succeeding
                    corporation.

          (4)  Effect on Stock Appreciation Rights and Other Stock Unit Awards.

          The Board may specify in an Award at the time of the grant the effect
of a Reorganization Event and Change in Control Event on any SAR and Other Stock
Unit Award.

10.  General Provisions Applicable to Awards

     (a) Transferability of Awards. Except as the Board may otherwise determine
or provide in an Award, Awards shall not be sold, assigned, transferred, pledged
or otherwise encumbered by the person to whom they are granted, either
voluntarily or by operation of law, except by will or the laws of descent and
distribution or, other than in the case of an Incentive Stock Option, pursuant
to a qualified domestic relations order, and, during the life of the
Participant, shall be exercisable only by the Participant. References to a
Participant, to the extent relevant in the context, shall include references to
authorized transferees.

     (b) Documentation. Each Award shall be evidenced in such form (written,
electronic or otherwise) as the Board shall determine. Each Award may contain
terms and conditions in addition to those set forth in the Plan.

     (c) Board Discretion. Except as otherwise provided by the Plan, each Award
may be made alone or in addition or in relation to any other Award. The terms of
each Award need not be identical, and the Board need not treat Participants
uniformly.

     (d) Termination of Status. The Board shall determine the effect on an Award
of the disability, death, retirement, authorized leave of absence or other
change in the employment or other status of a Participant and the extent to
which, and the period during which, the Participant, or the Participant's legal
representative, conservator, guardian or Designated Beneficiary, may exercise
rights under the Award.

                                      -12-
<PAGE>
     (e) Withholding. Each Participant shall pay to the Company, or make
provision satisfactory to the Company for payment of, any taxes required by law
to be withheld in connection with an Award to such Participant. Except as the
Board may otherwise provide in an Award, for so long as the Common Stock is
registered under the Exchange Act, Participants may satisfy such tax obligations
in whole or in part by delivery of shares of Common Stock, including shares
retained from the Award creating the tax obligation, valued at their Fair Market
Value; provided, however, except as otherwise provided by the Board, that the
total tax withholding where stock is being used to satisfy such tax obligations
cannot exceed the Company's minimum statutory withholding obligations (based on
minimum statutory withholding rates for federal and state tax purposes,
including payroll taxes, that are applicable to such supplemental taxable
income). Shares surrendered to satisfy tax withholding requirements cannot be
subject to any repurchase, forfeiture, unfulfilled vesting or other similar
requirements. The Company may, to the extent permitted by law, deduct any such
tax obligations from any payment of any kind otherwise due to a Participant.

     (f) Amendment of Award. The Board may amend, modify or terminate any
outstanding Award, including but not limited to, substituting therefor another
Award of the same or a different type, changing the date of exercise or
realization, and converting an Incentive Stock Option to a Nonstatutory Stock
Option, provided that the Participant's consent to such action shall be required
unless the Board determines that the action, taking into account any related
action, would not materially and adversely affect the Participant.

     (g) Conditions on Delivery of Stock. The Company will not be obligated to
deliver any shares of Common Stock pursuant to the Plan or to remove
restrictions from shares previously delivered under the Plan until (i) all
conditions of the Award have been met or removed to the satisfaction of the
Company, (ii) in the opinion of the Company's counsel, all other legal matters
in connection with the issuance and delivery of such shares have been satisfied,
including any applicable securities laws and any applicable stock exchange or
stock market rules and regulations, and (iii) the Participant has executed and
delivered to the Company such representations or agreements as the Company may
consider appropriate to satisfy the requirements of any applicable laws, rules
or regulations.

     (h) Acceleration. The Board may at any time provide that any Award shall
become immediately exercisable in full or in part, free of some or all
restrictions or conditions, or otherwise realizable in full or in part, as the
case may be.

11.  Miscellaneous

     (a) No Right To Employment or Other Status. No person shall have any claim
or right to be granted an Award, and the grant of an Award shall not be
construed as giving a Participant the right to continued employment or any other
relationship with the Company. The Company expressly reserves the right at any
time to dismiss or otherwise terminate its relationship with a Participant free
from any liability or claim under the Plan, except as expressly provided in the
applicable Award.

                                      -13-
<PAGE>
     (b) No Rights As Stockholder. Subject to the provisions of the applicable
Award, no Participant or Designated Beneficiary shall have any rights as a
stockholder with respect to any shares of Common Stock to be distributed with
respect to an Award until becoming the record holder of such shares.
Notwithstanding the foregoing, in the event the Company effects a split of the
Common Stock by means of a stock dividend and the exercise price of and the
number of shares subject to such Option are adjusted as of the date of the
distribution of the dividend (rather than as of the record date for such
dividend), then an optionee who exercises an Option between the record date and
the distribution date for such stock dividend shall be entitled to receive, on
the distribution date, the stock dividend with respect to the shares of Common
Stock acquired upon such Option exercise, notwithstanding the fact that such
shares were not outstanding as of the close of business on the record date for
such stock dividend.

     (c) Effective Date and Term of Plan. The Plan shall become effective on the
date on which it is adopted by the Board. No Awards shall be granted under the
Plan after the completion of 10 years from the earlier of (i) the date on which
the Plan was adopted by the Board or (ii) the date the Plan was approved by the
Company's stockholders, but Awards previously granted may extend beyond that
date.

     (d) Amendment of Plan. The Board may amend, suspend or terminate the Plan
or any portion thereof at any time; provided that, to the extent determined by
the Board, no amendment requiring stockholder approval under any applicable
legal, regulatory or listing requirement shall become effective until such
stockholder approval is obtained.

     (e) Authorization of Sub-Plans. The Board may from time to time establish
one or more sub-plans under the Plan for purposes of satisfying applicable blue
sky, securities or tax laws of various jurisdictions. The Board shall establish
such sub-plans by adopting supplements to this Plan containing (i) such
limitations on the Board's discretion under the Plan as the Board deems
necessary or desirable or (ii) such additional terms and conditions not
otherwise inconsistent with the Plan as the Board shall deem necessary or
desirable. All supplements adopted by the Board shall be deemed to be part of
the Plan, but each supplement shall apply only to Participants within the
affected jurisdiction and the Company shall not be required to provide copies of
any supplement to Participants in any jurisdiction which is not the subject of
such supplement.

     (f) Compliance with Code Section 409A. No Award shall provide for deferral
of compensation that does not comply with Section 409A of the Code, unless the
Board, at the time of grant, specifically provides that the Award is not
intended to comply with Section 409A of the Code.

     (g) Governing Law. The provisions of the Plan and all Awards made hereunder
shall be governed by and interpreted in accordance with the laws of the State of
Delaware, excluding choice-of-law principles of the law of such state that would
require the application of the laws of a jurisdiction other than such state.

                                      -14-
<PAGE>
                                        Adopted by the Board of Directors
                                        on September 7, 2005

                                        Approved by the stockholders on
                                        October 14, 2005, 2005

                                      -15-
<PAGE>
                              NxStage Medical, Inc.

                        Incentive Stock Option Agreement
                     Granted Under 2005 Stock Incentive Plan

1.   Grant of Option.

     This agreement evidences the grant by NxStage Medical, Inc., a Delaware
corporation (the "Company"), on __________, 200[_] (the "Grant Date") to
[_________________], an employee of the Company (the "Participant"), of an
option to purchase, in whole or in part, on the terms provided herein and in the
Company's 2005 Stock Incentive Plan (the "Plan"), a total of [____________]
shares (the "Shares") of common stock, $0.001 par value per share, of the
Company ("Common Stock") at $[_____________] per Share. Unless earlier
terminated, this option shall expire at 5:00 p.m., Eastern time, on [_______]
(the "Final Exercise Date").

     It is intended that the option evidenced by this agreement shall be an
incentive stock option as defined in Section 422 of the Internal Revenue Code of
1986, as amended, and any regulations promulgated thereunder (the "Code").
Except as otherwise indicated by the context, the term "Participant", as used in
this option, shall be deemed to include any person who acquires the right to
exercise this option validly under its terms.

2.   Vesting Schedule.

     This option will become exercisable ("vest") as to ________% of the
original number of Shares on the [first] anniversary of the Grant Date and as to
an additional ________% of the original number of Shares at the end of each
successive [three-month] period following the first anniversary of the Grant
Date until the [fourth] anniversary of the Grant Date.

     The right of exercise shall be cumulative so that to the extent the option
is not exercised in any period to the maximum extent permissible it shall
continue to be exercisable, in whole or in part, with respect to all Shares for
which it is vested until the earlier of the Final Exercise Date or the
termination of this option under Section 3 hereof or the Plan.

3.   Exercise of Option.

     (a) Form of Exercise. Each election to exercise this option shall be in
writing, signed by the Participant, and received by the Company at its principal
office, accompanied by this agreement, and payment in full in the manner
provided in the Plan. The Participant may purchase less than the number of
shares covered hereby, provided that no partial exercise of this option may be
for any fractional share or for fewer than ten whole shares.

     (b) Continuous Relationship with the Company Required. Except as otherwise
provided in this Section 3, this option may not be exercised unless the
Participant, at the time he or she exercises this option, is, and has been at
all times since the Grant Date, an employee or officer of, or consultant or
advisor to, the Company or any parent or subsidiary of the Company as defined in
Section 424(e) or (f) of the Code (an "Eligible Participant").
<PAGE>
     (c) Termination of Relationship with the Company. If the Participant ceases
to be an Eligible Participant for any reason, then, except as provided in
paragraphs (d) and (e) below, the right to exercise this option shall terminate
three months after such cessation (but in no event after the Final Exercise
Date), provided that this option shall be exercisable only to the extent that
the Participant was entitled to exercise this option on the date of such
cessation. Notwithstanding the foregoing, if the Participant, prior to the Final
Exercise Date, violates the non-competition or confidentiality provisions of any
employment contract, confidentiality and nondisclosure agreement or other
agreement between the Participant and the Company, the right to exercise this
option shall terminate immediately upon such violation.

     (d) Exercise Period Upon Death or Disability. If the Participant dies or
becomes disabled (within the meaning of Section 22(e)(3) of the Code) prior to
the Final Exercise Date while he or she is an Eligible Participant and the
Company has not terminated such relationship for "cause" as specified in
paragraph (e) below, this option shall be exercisable, within the period of one
year following the date of death or disability of the Participant, by the
Participant (or in the case of death by an authorized transferee), provided that
this option shall be exercisable only to the extent that this option was
exercisable by the Participant on the date of his or her death or disability,
and further provided that this option shall not be exercisable after the Final
Exercise Date.

     (e) Termination for Cause. If, prior to the Final Exercise Date, the
Participant's employment is terminated by the Company for Cause (as defined
below), the right to exercise this option shall terminate immediately upon the
effective date of such termination of employment. If the Participant is party to
an employment or severance agreement with the Company that contains a definition
of "cause" for termination of employment, "Cause" shall have the meaning
ascribed to such term in such agreement. Otherwise, "Cause" shall mean willful
misconduct by the Participant or willful failure by the Participant to perform
his or her responsibilities to the Company (including, without limitation,
breach by the Participant of any provision of any employment, consulting,
advisory, nondisclosure, non-competition or other similar agreement between the
Participant and the Company), as determined by the Company, which determination
shall be conclusive. The Participant shall be considered to have been discharged
for Cause if the Company determines, within 30 days after the Participant's
resignation, that discharge for cause was warranted.

4.   Tax Matters.

     (a) Withholding. No Shares will be issued pursuant to the exercise of this
option unless and until the Participant pays to the Company, or makes provision
satisfactory to the Company for payment of, any federal, state or local
withholding taxes required by law to be withheld in respect of this option.

     (b) Disqualifying Disposition. If the Participant disposes of Shares
acquired upon exercise of this option within two years from the Grant Date or
one year after such Shares were acquired pursuant to exercise of this option,
the Participant shall notify the Company in writing of such disposition.

                                       -2-
<PAGE>
5.   Nontransferability of Option.

     This option may not be sold, assigned, transferred, pledged or otherwise
encumbered by the Participant, either voluntarily or by operation of law, except
by will or the laws of descent and distribution, and, during the lifetime of the
Participant, this option shall be exercisable only by the Participant.

6.   Provisions of the Plan.

     This option is subject to the provisions of the Plan, a copy of which is
furnished to the Participant with this option.

     IN WITNESS WHEREOF, the Company has caused this option to be executed under
its corporate seal by its duly authorized officer. This option shall take effect
as a sealed instrument.

                                        NxStage Medical, Inc.

Dated:                                  By:
       -----------                          ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                       -3-
<PAGE>
                            PARTICIPANT'S ACCEPTANCE

     The undersigned hereby accepts the foregoing option and agrees to the terms
and conditions thereof. The undersigned hereby acknowledges receipt of a copy of
the Company's 2005 Stock Incentive Plan.

                                        PARTICIPANT:

                                        ----------------------------------------
                                        Address:
                                                 -------------------------------

                                                 -------------------------------

                                       -4-
<PAGE>
                              NxStage Medical, Inc.

                       Nonstatutory Stock Option Agreement
                     Granted Under 2005 Stock Incentive Plan

1.   Grant of Option.

     This agreement evidences the grant by NxStage Medical, Inc., a Delaware
corporation (the "Company"), on __________, 200[_] (the "Grant Date") to
[__________], an [employee], [consultant], [director] of the Company (the
"Participant"), of an option to purchase, in whole or in part, on the terms
provided herein and in the Company's 2005 Stock Incentive Plan (the "Plan"), a
total of [_________] shares (the "Shares") of common stock, $0.001 par value per
share, of the Company ("Common Stock") at $[___________] per Share. Unless
earlier terminated, this option shall expire at 5:00 p.m., Eastern time, on
[_______] (the "Final Exercise Date").

     It is intended that the option evidenced by this agreement shall not be an
incentive stock option as defined in Section 422 of the Internal Revenue Code of
1986, as amended, and any regulations promulgated thereunder (the "Code").
Except as otherwise indicated by the context, the term "Participant," as used in
this option, shall be deemed to include any person who acquires the right to
exercise this option validly under its terms.

2.   Vesting Schedule.

     This option will become exercisable ("vest") as to _________% of the
original number of Shares on the [first] anniversary of the Grant Date and as to
an additional ________% of the original number of Shares at the end of each
successive [three-month] period following the first anniversary of the Grant
Date until the [fourth] anniversary of the Grant Date.

     The right of exercise shall be cumulative so that to the extent the option
is not exercised in any period to the maximum extent permissible it shall
continue to be exercisable, in whole or in part, with respect to all Shares for
which it is vested until the earlier of the Final Exercise Date or the
termination of this option under Section 3 hereof or the Plan.

3.   Exercise of Option.

     (a) Form of Exercise. Each election to exercise this option shall be in
writing, signed by the Participant, and received by the Company at its principal
office, accompanied by this agreement, and payment in full in the manner
provided in the Plan. The Participant may purchase less than the number of
shares covered hereby, provided that no partial exercise of this option may be
for any fractional share or for fewer than ten whole shares.

     (b) Continuous Relationship with the Company Required. Except as otherwise
provided in this Section 3, this option may not be exercised unless the
Participant, at the time he or she exercises this option, is, and has been at
all times since the Grant Date, an employee, officer or director of, or
consultant or advisor to, the Company or any other entity the employees,
officers, directors, consultants, or advisors of which are eligible to receive
option grants under the Plan (an "Eligible Participant").
<PAGE>
     (c) Termination of Relationship with the Company. If the Participant ceases
to be an Eligible Participant for any reason, then, except as provided in
paragraphs (d) and (e) below, the right to exercise this option shall terminate
three months after such cessation (but in no event after the Final Exercise
Date), provided that this option shall be exercisable only to the extent that
the Participant was entitled to exercise this option on the date of such
cessation. Notwithstanding the foregoing, if the Participant, prior to the Final
Exercise Date, violates the non-competition or confidentiality provisions of any
employment contract, confidentiality and nondisclosure agreement or other
agreement between the Participant and the Company, the right to exercise this
option shall terminate immediately upon such violation.

     (d) Exercise Period Upon Death or Disability. If the Participant dies or
becomes disabled (within the meaning of Section 22(e)(3) of the Code) prior to
the Final Exercise Date while he or she is an Eligible Participant and the
Company has not terminated such relationship for "cause" as specified in
paragraph (e) below, this option shall be exercisable, within the period of one
year following the date of death or disability of the Participant, by the
Participant (or in the case of death by an authorized transferee), provided that
this option shall be exercisable only to the extent that this option was
exercisable by the Participant on the date of his or her death or disability,
and further provided that this option shall not be exercisable after the Final
Exercise Date.

     (e) Termination for Cause. If, prior to the Final Exercise Date, the
Participant's employment or other relationship with the Company is terminated by
the Company for Cause (as defined below), the right to exercise this option
shall terminate immediately upon the effective date of such termination of
employment or other relationship. If the Participant is party to an employment,
consulting or severance agreement with the Company that contains a definition of
"cause" for termination of employment or other relationship, "Cause" shall have
the meaning ascribed to such term in such agreement. Otherwise, "Cause" shall
mean willful misconduct by the Participant or willful failure by the Participant
to perform his or her responsibilities to the Company (including, without
limitation, breach by the Participant of any provision of any employment,
consulting, advisory, nondisclosure, non-competition or other similar agreement
between the Participant and the Company), as determined by the Company, which
determination shall be conclusive. The Participant shall be considered to have
been discharged for "Cause" if the Company determines, within 30 days after the
Participant's resignation, that discharge for cause was warranted.

4.   Withholding.

     No Shares will be issued pursuant to the exercise of this option unless and
until the Participant pays to the Company, or makes provision satisfactory to
the Company for payment of, any federal, state or local withholding taxes
required by law to be withheld in respect of this option.

5.   Nontransferability of Option.

     This option may not be sold, assigned, transferred, pledged or otherwise
encumbered by the Participant, either voluntarily or by operation of law, except
by will or the laws of descent

                                       -2-
<PAGE>
and distribution, and, during the lifetime of the Participant, this option shall
be exercisable only by the Participant.

6.   Provisions of the Plan.

     This option is subject to the provisions of the Plan, a copy of which is
furnished to the Participant with this option.

     IN WITNESS WHEREOF, the Company has caused this option to be executed under
its corporate seal by its duly authorized officer. This option shall take effect
as a sealed instrument.

                                        NxStage Medical, Inc.

Dated:                                  By:
       -----------                          ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                       -3-
<PAGE>
                            PARTICIPANT'S ACCEPTANCE

     The undersigned hereby accepts the foregoing option and agrees to the terms
and conditions thereof. The undersigned hereby acknowledges receipt of a copy of
the Company's 2005 Stock Incentive Plan.

                                        PARTICIPANT:

                                        ----------------------------------------
                                        Address:
                                                 -------------------------------

                                                 -------------------------------

                                       -4-<PAGE>

                                                                   Exhibit 10.23

                              EMPLOYMENT AGREEMENT
                                  DAVID N. GILL

      THIS EMPLOYMENT AGREEMENT (the "Agreement") is entered into this 19th day
of October, 2005 (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 David N. Gill, of 8513 River Club
Way, Knoxville, TN 37922 (the "Executive").

      WHEREAS, the Company desires to continue to employ Executive, and
Executive desires to continue 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 continue 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. Commencing on the Effective Date,
Executive shall continue to 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.

<PAGE>

      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
$225,000, 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. For 2005, the Board and the compensation committee have
determined that Executive will be entitled to receive incentive compensation of
up to 25% of Executive's 2005 base salary 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

                                       2
<PAGE>

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 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 .75 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 9-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. In addition, in the event of a termination of the Executive
pursuant to 2.1(a) on or before October 8, 2006, Executive's stock awards shall
vest such that Executive shall be at least 50% vested in the options granted to
him on July 8, 2005 at the expiration of the Severance Period. Subject to the
provisions of Section 2.2(a) below, Executive shall have up to one hundred and
eighty (180) 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

                                       3
<PAGE>

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.

                  (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) 1.5 times Executive's annual Base Salary at the rate in
effect at the time of Executive's termination, plus (B) 1.5 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 18-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

                                       4
<PAGE>

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.

                  (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 granted to
Executive shall become fully vested and exercisable on the date of the Change of
Control. Executive shall have up to one hundred and eighty (180) 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
one hundred and eighty (180) 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

                                       5
<PAGE>

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).

            (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.

                                       6
<PAGE>

      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
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

                                       7
<PAGE>

                  (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:

                  (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

                                       8
<PAGE>

residence (as defined by Section 217 of the Code) 50 miles from the Executive's
principal office).

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:

                                       9
<PAGE>

      David N. Gill
      8513 River Club Way
      Knoxville, TN 37922

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.

                                       10
<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.

                                       11
<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/ David N. Gill
                                               --------------------------------

                                               Name: David N. Gill

                                       12

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