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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.


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<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-