Document:

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                                                                   Exhibit 10.32

                          REGISTRATION RIGHTS AGREEMENT

         This Registration Rights Agreement (this "Agreement") is made and
entered into as of February 7, 2007, by and among NxStage Medical, Inc., a
Delaware corporation (the "Company"), and DaVita Inc., a Delaware corporation
(the "Purchaser").

         This Agreement is made pursuant to, and as a condition to closing
under, the Stock Purchase Agreement, dated as of the date hereof among the
Company and the Purchaser (the "Purchase Agreement").

         The Company and the Purchaser hereby agree as follows:

1.       Definitions.  Capitalized terms used and not otherwise defined herein
that are defined in the Purchase Agreement shall have the meanings given such
terms in the Purchase Agreement. As used in this Agreement, the following terms
shall have the following meanings:

                  "Commission" means the Securities and Exchange Commission.

                  "Effectiveness Date" means, with respect to the initial
         Registration Statement required to be filed hereunder, the 120th
         calendar day following the Closing Date.

                  "Effectiveness Period" shall have the meaning set forth in
         Section 2(a).

                  "Exchange Act" means the Securities Exchange Act of 1934, as
         amended.

                  "Filing Date" means, the 90th calendar day following the
         Closing Date.

                  "Holder" shall have the meaning ascribed to it in the Investor
         Rights Agreement.

                  "Indemnified Party" shall have the meaning set forth in
         Section 5(c).

                  "Indemnifying Party" shall have the meaning set forth in
         Section 5(c).

                  "Investor Rights Agreement" shall mean the Investor Rights
         Agreement, dated as of June 30, 1999, by and between the Company and
         the investors listed thereon, as amended to date, a copy of which is
         attached hereto as Exhibit A.

                  "Losses" shall have the meaning set forth in Section 5(a).

                  "Proceeding" means an action, claim, suit, investigation or
         proceeding (including, without limitation, an investigation or partial
         proceeding, such as a deposition), whether commenced or threatened.

                  "Prospectus" means the prospectus included in the Registration
         Statement (including, without limitation, a prospectus that includes
         any information previously

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         omitted from a prospectus filed as part of an effective registration
         statement in reliance upon Rule 430A promulgated under the Securities
         Act), as amended or supplemented by any prospectus supplement, with
         respect to the terms of the offering of any portion of the Registrable
         Securities covered by the Registration Statement, and all other
         amendments and supplements to the Prospectus, including post-effective
         amendments, and all material incorporated by reference or deemed to be
         incorporated by reference in such Prospectus.

                  "Registrable Securities" means the Shares, together with any
         securities issued or issuable upon any stock split, dividend or other
         distribution, recapitalization or similar event with respect to the
         foregoing.

                  "Purchaser Registration Statement" means the Purchaser
         Registration Statements required to be filed under Section 2, including
         (in each case) the Prospectus, amendments and supplements to such
         registration statement or Prospectus, including pre- and post-effective
         amendments, all exhibits thereto, and all material incorporated by
         reference or deemed to be incorporated by reference in such
         registration statement.

                  "Rule 415" means Rule 415 promulgated by the Commission
         pursuant to the Securities Act, as such Rule may be amended from time
         to time, or any similar rule or regulation hereafter adopted by the
         Commission having substantially the same effect as such Rule.

                  "Rule 424" means Rule 424 promulgated by the Commission
         pursuant to the Securities Act, as such Rule may be amended from time
         to time, or any similar rule or regulation hereafter adopted by the
         Commission having substantially the same effect as such Rule.

                  "Securities Act" means the Securities Act of 1933, as amended.

                  "Shares" solely for the purpose of this Agreement means the
         Shares (as defined in the Purchase Agreement).

2.       Purchaser Registration.

         (a)      On or prior to the Filing Date, the Company shall use best
efforts to prepare and file with the Commission the Purchaser Registration
Statement covering the resale by the Purchaser to the public of the Registrable
Securities for an offering to be made on a continuous basis pursuant to Rule
415. The Purchaser Registration Statement required hereunder shall be on Form
S-3 (except if the Company is not then eligible to register for resale the
Registrable Securities on Form S-3, in which case such registration shall be on
another appropriate form in accordance herewith). The Purchaser Registration
Statement shall contain (except if otherwise required pursuant to comments
received from the Commission upon a review of the Purchaser Registration
Statement) the "Plan of Distribution" attached hereto as Annex A. The Company
shall use its best efforts to cause the Purchaser Registration Statement to be
declared effective under the Securities Act as promptly as possible after the
filing thereof, but in any event not later than the Effectiveness Date, and
shall use commercially reasonable efforts to keep the Purchaser Registration
Statement continuously effective under the Securities Act until the date which
is the

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earliest of (i) two years after the date the Purchaser Registration Statement is
declared effective by the Commission (ii) such time as all the Registrable
Securities covered by the Purchaser Registration Statement have been publicly
sold or (iii) such time as all the Registrable Securities may be sold pursuant
to Rule 144(k) without volume restrictions as determined by the counsel to the
Company pursuant to a written opinion letter to such effect, addressed and
acceptable to the Company's transfer agent and the Purchaser (the "Effectiveness
Period").

         (b)      If the Purchaser Registration Statement (i) is not declared
effective by the Commission on or before the Effectiveness Date or (ii) ceases
to remain effective at any time during the Effectiveness Period for more than an
aggregate of 15 Trading Days (any such failure or breach to be referred to as an
"Event" and for purposes of clause (i) the date on which such event occurs, and
for the purposes of clause (ii) the date on which such 15 Trading Day period is
exceeded, being referred to as the "Event Date") then in addition to any other
rights the Purchaser may have hereunder or under applicable law: (x) on the
seventh day after the Event Date, the Company shall make a payment to the
Purchaser of an amount in cash, as liquidated damages and not as a penalty,
equal to 1.0% of the aggregate purchase price paid by the Purchaser pursuant to
the Purchase Agreement for any Registrable Securities then held by the
Purchaser; and (y) on each monthly anniversary of each such Event Date (if the
applicable Event shall not have been cured by such date) until the applicable
Event is cured, the Company shall make a pro rata payment to the Purchaser in an
amount in cash, as liquidated damages and not as a penalty, equal to 1.0% of the
aggregate purchase price paid by the Purchaser pursuant to the Purchase
Agreement for any Registrable Securities then held by the Purchaser for each
month or pro rata portion thereof until the applicable Event is cured.

         (c)      The Purchaser agrees to furnish to the Company a completed
Questionnaire in the form attached to this Agreement as Annex B, or other form
reasonably acceptable to the Company (a "Selling Holder Questionnaire"). The
Company shall not be required to include the Registrable Securities in the
Purchaser Registration Statement and shall not be required to pay any liquidated
or other damages under Section 2(b) to the Purchaser if it fails to furnish to
the Company a fully completed Selling Holder Questionnaire at least two Trading
Days prior to the Filing Date (subject to the requirements set forth in Section
3(a)).

         (d)      If the Purchaser intends to distribute the Registrable
Securities by means of an underwriting, Purchaser shall promptly so advise the
Company. Purchaser and Company shall enter into an underwriting agreement in
usual and customary form with the underwriter or underwriters selected for such
underwriting by the Purchaser (which underwriter or underwriters shall be
reasonably acceptable to the Company).

3.       Registration Procedures.

         In connection with the Company's registration obligations under Section
2, the Company shall:

         (a)      Not less than three Trading Days prior to the filing of the
Purchaser Registration Statement or any related Prospectus or any amendment or
supplement thereto, (i) furnish to the Purchaser copies of all such documents
proposed to be filed (including documents incorporated

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or deemed incorporated by reference to the extent requested by the Purchaser)
which documents will be subject to the review of the Purchasers, and (ii) cause
its officers and directors, counsel and independent certified public accountants
to respond to such inquiries as shall be necessary, in the reasonable opinion of
respective counsel to conduct a reasonable investigation within the meaning of
the Securities Act. The Company shall not file the Purchaser Registration
Statement or any such Prospectus or any amendments or supplements thereto, to
which the Purchaser shall reasonably object.

         (b)      (i) Prepare and file with the Commission such amendments,
including post-effective amendments, to the Purchaser Registration Statement and
the Prospectus used in connection therewith as may be necessary to keep the
Purchaser Registration Statement continuously effective as to the applicable
Registrable Securities for the Effectiveness Period; (ii) cause the related
Prospectus to be amended or supplemented by any required Prospectus supplement,
and as so supplemented or amended to be filed pursuant to Rule 424; (iii)
respond as promptly as reasonably possible to any comments received from the
Commission with respect to the Purchaser Registration Statement or any amendment
thereto and, as promptly as reasonably possible, upon request, provide the
Purchaser true and complete copies of all correspondence from and to the
Commission relating to such Purchaser Registration Statement that would not
result in the disclosure to the Purchaser of material and non-public information
concerning the Company; and (iv) comply in all material respects with the
provisions of the Securities Act and the Exchange Act with respect to the
disposition of all Registrable Securities covered by the Purchaser Registration
Statement during the applicable period.

         (c)      Notify the Purchaser as promptly as reasonably possible (and,
in the case of (i)(A) below, not less than three Trading Days prior to such
filing) and (if requested by the Purchaser) confirm such notice in writing
promptly following the day (i)(A) when a Prospectus or any Prospectus supplement
or post-effective amendment to the Purchaser Registration Statement is proposed
to be filed; (B) when the Commission notifies the Company whether there will be
a "review" of the Purchaser Registration Statement and whenever the Commission
comments in writing on such Purchaser Registration Statement (the Company shall
upon request provide true and complete copies thereof and all written responses
thereto that would not result in the disclosure to the Purchaser of material and
non-public information concerning the Company); and (C) with respect to the
Purchaser Registration Statement or any post-effective amendment, when the same
has become effective; (ii) of any request by the Commission or any other federal
or state governmental authority during the Effectiveness Period for amendments
or supplements to the Purchaser Registration Statement or Prospectus or for
additional information; (iii) of the issuance by the Commission or any other
federal or state governmental authority of any stop order suspending the
effectiveness of the Purchaser Registration Statement covering any or all of the
Registrable Securities or the initiation of any Proceedings for that purpose;
(iv) of the receipt by the Company of any notification with respect to the
suspension of the qualification or exemption from qualification of any of the
Registrable Securities for sale in any jurisdiction, or the initiation or
threatening of any Proceeding for such purpose; and (v) of the occurrence of any
event or passage of time that makes the financial statements included in the
Purchaser Registration Statement ineligible for inclusion therein or any
statement made in such Purchaser Registration Statement or Prospectus or any
document incorporated or deemed to be incorporated therein by reference untrue
in any material respect or that requires any revisions to

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the Purchaser Registration Statement, Prospectus or other documents so that, in
the case of the Purchaser Registration Statement or the Prospectus, as the case
may be, it will not contain any untrue statement of a material fact or omit to
state any material fact required to be stated therein or necessary to make the
statements therein, in light of the circumstances under which they were made,
not misleading.

         (d)      Use its best efforts to avoid the issuance of, or, if issued,
obtain the withdrawal of (i) any order suspending the effectiveness of the
Purchaser Registration Statement, or (ii) any suspension of the qualification
(or exemption from qualification) of any of the Registrable Securities for sale
in any jurisdiction, at the earliest practicable moment.

         (e)      Furnish to the Purchaser, without charge, at least one
conformed copy of each Purchaser Registration Statement and each amendment
thereto, and all exhibits to the extent requested by the Purchaser (including
those previously furnished) promptly after the filing of such documents with the
Commission.

         (f)      Promptly deliver to the Purchaser, without charge, as many
copies of the Prospectus or Prospectuses (including each form of prospectus) and
each amendment or supplement thereto as the Purchaser may reasonably request.
The Company hereby consents to the use of such Prospectus and each amendment or
supplement thereto by the Purchaser in connection with the offering and sale of
the Registrable Securities covered by such Prospectus and any amendment or
supplement thereto.

         (g)      Prior to any public offering of Registrable Securities, use
commercially reasonable efforts to register or qualify or cooperate with the
Purchaser in connection with the registration or qualification (or exemption
from such registration or qualification) of such Registrable Securities for
offer and sale under the securities or Blue Sky laws of such jurisdictions
within the United States as the Purchaser reasonably requests in writing, to
keep each such registration or qualification (or exemption therefrom) effective
during the Effectiveness Period and to do any and all other acts or things
reasonably necessary or advisable to enable the disposition in such
jurisdictions of the Registrable Securities covered by the Purchaser
Registration Statement; provided, that the Company shall not be required to
qualify generally to do business in any jurisdiction where it is not then so
qualified, subject the Company to any material tax in any such jurisdiction
where it is not then so subject or file a general consent to service of process
in any such jurisdiction.

         (h)      Cooperate with the Purchaser to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be delivered to a transferee pursuant to the Purchaser Registration Statement,
which certificates shall be free, to the extent permitted by the Purchase
Agreement, of all restrictive legends, and to enable such Registrable Securities
to be in such denominations and registered in such names as the Purchaser may
request.

         (i)      Upon the occurrence of any event contemplated by Section
3(c)(v), as promptly as reasonably possible, prepare a supplement or amendment,
including a post-effective amendment if necessary, to the Purchaser Registration
Statement or a supplement to the related Prospectus or any document incorporated
or deemed to be incorporated therein by reference, and

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file any other required document so that, as thereafter delivered, neither the
Purchaser Registration Statement nor the Prospectus will contain an untrue
statement of a material fact or omit to state a material fact required to be
stated therein or necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading.

         (j)      In the event of any underwritten public offering of the
Registrable Securities, cooperate with and enter into and perform its
obligations under an underwriting agreement, in usual and customary form, with
the managing underwriter(s) of such offering.

4.       Registration Expenses.

         All reasonable expenses, other than underwriting discounts, commissions
or concessions and brokers' or agents' commissions or concessions or selling
commissions or concessions, incurred in connection with registrations, filings
or qualifications pursuant to this Agreement, including, without limitation, all
registration, listing and qualifications fees, printers and accounting fees, and
fees and disbursements of counsel for Company shall be paid by Company. The
Purchaser shall pay any and all fees and disbursements of legal counsel for the
Purchaser in connection with registration, filing or qualification of the
Registrable Securities pursuant to this Agreement. Notwithstanding anything to
the contrary contained herein, all expenses incurred in connection with a
registration under Section 7 below, will be borne in accordance with the
Investor Rights Agreement.

5.       Indemnification.

         (a)      Indemnification by the Company. The Company shall,
notwithstanding any termination of this Agreement, indemnify and hold harmless
the Purchaser, its officers, directors, agents and employees, each person or
entity who controls the Purchaser (within the meaning of Section 15 of the
Securities Act or Section 20 of the Exchange Act) and the officers, directors,
agents and employees of each such controlling person or entity, to the fullest
extent permitted by applicable law, from and against any and all losses, claims,
damages, liabilities, costs (including, without limitation, reasonable
attorneys' fees) and expenses (collectively, "Losses"), as incurred, arising out
of or relating to (i) any material violation by the Company of Federal or state
securities law, or any other law or regulation relating to the offer or sale of
the Registrable Securities pursuant to the Purchaser Registration Statement;
(ii) any untrue or alleged untrue statement of a material fact contained in the
Purchaser Registration Statement, any Prospectus or any form of prospectus or in
any amendment or supplement thereto or in any preliminary prospectus, or (iii)
any omission or alleged omission of a material fact required to be stated
therein or necessary to make the statements therein (in the case of any
Prospectus or form of prospectus or supplement thereto, in light of the
circumstances under which they were made) not misleading, except to the extent,
but only to the extent, that (1) such untrue statements or omissions are based
solely upon information regarding the Purchaser furnished in writing to the
Company by the Purchaser expressly for use therein, or to the extent that such
information relates to the Purchaser or the Purchaser's proposed method of
distribution of Registrable Securities and was reviewed and expressly approved
in writing by the Purchaser expressly for use in the Purchaser Registration
Statement, such Prospectus or such form of Prospectus or in any amendment or
supplement thereto (it being understood that the Purchaser has approved Annex A
hereto for this purpose) or (2) in the case of an occurrence of an event of the
type

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specified in Section 3(c)(ii)-(v), the use by the Purchaser of an outdated or
defective Prospectus after the Company has notified the Purchaser in writing
that the Prospectus is outdated or defective and prior to the receipt by the
Purchaser of the Advice contemplated in Section 8(d). The Company shall notify
the Purchaser promptly of the institution, threat or assertion of any Proceeding
of which the Company is aware in connection with the transactions contemplated
by this Agreement.

         (b)      Indemnification by the Purchaser. The Purchaser shall
indemnify and hold harmless the Company, its directors, officers, agents and
employees, each person or entity who controls the Company (within the meaning of
Section 15 of the Securities Act and Section 20 of the Exchange Act), and the
directors, officers, agents or employees of such controlling persons and
entities, to the fullest extent permitted by applicable law, from and against
all Losses, as incurred, arising out of or based solely upon: (x) the
Purchaser's failure to comply with the prospectus delivery requirements of the
Securities Act or (y) any untrue or alleged untrue statement of a material fact
contained in any Purchaser Registration Statement, any Prospectus, or any form
of prospectus, or in any amendment or supplement thereto or in any preliminary
prospectus, or arising out of or relating to any omission or alleged omission of
a material fact required to be stated therein or necessary to make the
statements therein not misleading (i) to the extent, but only to the extent,
that such untrue statement or omission is contained in any information so
furnished in writing by the Purchaser to the Company specifically for inclusion
in such Purchaser Registration Statement or such Prospectus or (ii) to the
extent that (1) such untrue statements or omissions are based upon information
regarding the Purchaser furnished in writing to the Company by the Purchaser
expressly for use therein, or to the extent that such information relates to the
Purchaser or the Purchaser's proposed method of distribution of Registrable
Securities and was reviewed and expressly approved in writing by the Purchaser
expressly for use in the Purchaser Registration Statement (it being understood
that the Purchaser has approved Annex A hereto for this purpose), such
Prospectus or such form of Prospectus or in any amendment or supplement thereto
or (2) in the case of an occurrence of an event of the type specified in Section
3(c)(ii)-(v), the use by the Purchaser of an outdated or defective Prospectus
after the Company has notified the Purchaser in writing that the Prospectus is
outdated or defective and prior to the receipt by the Purchaser of the Advice
contemplated in Section 8(d).

         (c)      Conduct of Indemnification Proceedings. If any Proceeding
shall be brought or asserted against any person or entity entitled to indemnity
hereunder (an "Indemnified Party"), such Indemnified Party shall promptly notify
the person or entity from whom indemnity is sought (the "Indemnifying Party") in
writing, and the Indemnifying Party shall have the right to assume the defense
thereof, including the employment of counsel reasonably satisfactory to the
Indemnified Party and the payment of all fees and expenses incurred in
connection with defense thereof; provided, that the failure of any Indemnified
Party to give such notice shall not relieve the Indemnifying Party of its
obligations or liabilities pursuant to this Agreement, except (and only) to the
extent that it shall be finally determined by a court of competent jurisdiction
(which determination is not subject to appeal or further review) that such
failure shall have prejudiced the Indemnifying Party.

         An Indemnified Party shall have the right to employ separate counsel in
any such Proceeding and to participate in the defense thereof, but the fees and
expenses of such counsel

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shall be at the expense of such Indemnified Party or Parties unless: (1) the
Indemnifying Party has agreed in writing to pay such fees and expenses; (2) the
Indemnifying Party shall have failed promptly to assume the defense of such
Proceeding and to employ counsel reasonably satisfactory to such Indemnified
Party in any such Proceeding; or (3) the named parties to any such Proceeding
(including any impleaded parties) include both such Indemnified Party and the
Indemnifying Party, and such Indemnified Party shall have been advised by
counsel that a conflict of interest is likely to exist if the same counsel were
to represent such Indemnified Party and the Indemnifying Party (in which case,
if such Indemnified Party notifies the Indemnifying Party in writing that it
elects to employ separate counsel at the expense of the Indemnifying Party, the
Indemnifying Party shall not have the right to assume the defense thereof and
the reasonable fees and expenses of one separate counsel shall be at the expense
of the Indemnifying Party). In no event shall the Indemnifying Party be liable
for fees and expenses of more than one counsel (in addition to any local
counsel) for all Indemnified Parties. The Indemnifying Party shall not be liable
for any settlement of any such Proceeding effected without its written consent,
which consent shall not be unreasonably withheld. No Indemnifying Party shall,
without the prior written consent of the Indemnified Party, effect any
settlement of any pending Proceeding in respect of which any Indemnified Party
is a party, unless such settlement includes an unconditional release of such
Indemnified Party from all liability on claims that are the subject matter of
such Proceeding.

         All reasonable fees and expenses of the Indemnified Party (including
reasonable fees and expenses to the extent incurred in connection with
investigating or preparing to defend such Proceeding in a manner not
inconsistent with this Section) shall be paid to the Indemnified Party, as
incurred, within thirty Trading Days of written notice thereof to the
Indemnifying Party; provided, that the Indemnified Party shall promptly
reimburse the Indemnifying Party for that portion of such fees and expenses
applicable to such actions for which such Indemnified Party is not entitled to
indemnification hereunder, determined based upon the relative faults of the
parties.

         (d)      Contribution. If a claim for indemnification under Section
5(a) or 5(b) is unavailable to an Indemnified Party (by reason of public policy
or otherwise), then each Indemnifying Party, in lieu of indemnifying such
Indemnified Party, shall contribute to the amount paid or payable by such
Indemnified Party as a result of such Losses, in such proportion as is
appropriate to reflect the relative fault of the Indemnifying Party and
Indemnified Party in connection with the actions, statements or omissions that
resulted in such Losses as well as any other relevant equitable considerations.
The relative fault of such Indemnifying Party and Indemnified Party shall be
determined by reference to, among other things, whether any action in question,
including any untrue or alleged untrue statement of a material fact or omission
or alleged omission of a material fact, has been taken or made by, or relates to
information supplied by, such Indemnifying Party or Indemnified Party, and the
parties' relative intent, knowledge, access to information and opportunity to
correct or prevent such action, statement or omission. The amount paid or
payable by a party as a result of any Losses shall be deemed to include, subject
to the limitations set forth in Section 5(c), any reasonable attorneys' or other
reasonable fees or expenses incurred by such party in connection with any
Proceeding to the extent such party would have been indemnified for such fees or
expenses if the indemnification provided for in this Section was available to
such party in accordance with its terms.

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         The parties hereto agree that it would not be just and equitable if
contribution pursuant to this Section 5(d) were determined by pro rata
allocation or by any other method of allocation that does not take into account
the equitable considerations referred to in the immediately preceding paragraph.
Notwithstanding the provisions of this Section 5(d), the Purchaser shall not be
required to contribute, in the aggregate, any amount in excess of the amount by
which the proceeds actually received by the Purchaser from the sale of the
Registrable Securities subject to the Proceeding exceeds the amount of any
damages that the Purchaser has otherwise been required to pay by reason of such
untrue or alleged untrue statement or omission or alleged omission, except in
the case of fraud by the Purchaser. No person or entity guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
will be entitled to contribution from any person or entity who was not guilty of
such fraudulent misrepresentation.

         Absent fraud or willful or intentional misconduct, the indemnification
and contribution provided by the Company and the Purchaser pursuant to this
Section 5 shall be the sole and exclusive remedy for any Losses referred to
herein. The amount of any payment by the Company under this Section 5 in respect
of any Losses resulting from or arising out of any indemnification or
contribution claim shall in no event exceed the gross proceeds to the Company as
a result of the sale of the Shares hereunder. The amount of any payment by the
Purchaser under this Section 5 in respect of any Losses resulting from or
arising out of any indemnification or contribution claim shall in no event
exceed the gross proceeds to such Purchaser as a result of the sale of the
Shares pursuant to the Purchaser Registration Statement.

         Further, the Company and the Purchaser agree that in no event shall
either party's aggregate liability under the Stock Purchase Agreement and this
Agreement exceed $20,000,000.

6.       Withdrawal of Purchaser Registration Statement. After the termination
of the Effectiveness Period, the Company shall be entitled to withdraw the
Purchaser Registration Statement, and the Purchasers shall have no further right
to offer or sell any of the Shares pursuant to the Purchaser Registration
Statement.

7.       Piggyback Registration Rights. In the event that, pursuant to Section
8(b) of the Purchase Agreement, the Company and the managing underwriter of a
public offering by the Company request that the Purchaser not sell or otherwise
transfer or dispose of any Shares or other securities of the Company held by the
Purchaser, the Purchaser may elect, for purposes of such offering only, to have
all the rights and obligations of a Holder under Section 2.3 of the Investor
Rights Agreement and, to the extent applicable to Section 2.3 only, Sections
2.5, 2.6, 2.7, 2.8, 2.9 and 2.11; provided, however, that the Purchaser must
also agree not to sell any Shares or other securities acquired of the Company
held by the Purchaser from the date of the filing of such registration statement
until 30 days following the effective date of such registration statement, other
than in connection with such offering. For the avoidance of doubt, except as
specifically set forth in this Section 7, the Purchaser shall have no rights or
obligations in connection with any offering by the Company nor shall it have any
rights or obligations, as a Holder or otherwise, under the Investor Rights
Agreement.

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8.       Miscellaneous.

         (a)      Remedies. In the event of a breach by the Company or by the
Purchaser, of any of their obligations under this Agreement, the Purchaser or
the Company, as the case may be, in addition to being entitled to exercise all
rights granted by law and under this Agreement, including recovery of damages,
will be entitled to specific performance of its rights under this Agreement. The
Company and the Purchaser agree that monetary damages would not provide adequate
compensation for any losses incurred by reason of a breach by it of any of the
provisions of this Agreement and hereby further agrees that, in the event of any
action for specific performance in respect of such breach, it shall waive the
defense that a remedy at law would be adequate.

         (b)      Registration of Other Securities. Notwithstanding anything
contained herein to the contrary and for the avoidance of doubt, the parties
hereto acknowledge that (a) the Company has granted registration rights to other
purchasers with respect its Common Stock, and (b) any Purchaser Registration
Statement prepared, filed and made effective under Section 3 may also cover the
resale of such other securities as well as any securities held by other security
holders which the Company has an obligation to register.

         (c)      Compliance. The Purchaser covenants and agrees that it will
comply with the prospectus delivery requirements of the Securities Act as
applicable to it in connection with sales of Registrable Securities pursuant to
the Purchaser Registration Statement.

         (d)      Discontinued Disposition. The Purchaser agrees that, upon
receipt of a notice from the Company of the occurrence of any event of the kind
described in Section 3(c), the Purchaser will forthwith discontinue disposition
of such Registrable Securities under the Purchaser Registration Statement until
the Purchaser's receipt of the copies of the supplemented Prospectus and/or
amended Purchaser Registration Statement or until it is advised in writing (the
"Advice") by the Company that the use of the applicable Prospectus may be
resumed, and, in either case, has received copies of any additional or
supplemental filings that are incorporated or deemed to be incorporated by
reference in such Prospectus or Purchaser Registration Statement. The Company
may provide appropriate stop orders to enforce the provisions of this paragraph.

         (e)      Amendments and Waivers. The provisions of this Agreement,
including the provisions of this sentence, may not be amended, modified or
supplemented, and waivers or consents to departures from the provisions hereof
may not be given, unless the same shall be in writing and signed by the Company
and the Purchaser.

         (f)      Notices. Any and all notices or other communications or
deliveries required or permitted to be provided hereunder shall be in writing
and shall be deemed given and effective on the earliest of (i) the date of
transmission, if such notice or communication is delivered via facsimile at the
facsimile number provided for below, (ii) the Trading Day following the date of
mailing, if sent by nationally recognized overnight courier service, or (iii)
upon actual receipt by the party to whom such notice is required to be given.
The address for such notices and communications shall be delivered and addressed
as set forth in the Purchase Agreement.

                                       10
<PAGE>

         (g)      Successors and Assigns. This Agreement shall inure to the
benefit of and be binding upon the successors and permitted assigns of each of
the parties. Except to its successors, the Company may not assign its rights or
obligations hereunder without the prior written consent of the Purchaser.

         (h)      Execution and Counterparts. This Agreement may be executed in
any number of counterparts, each of which when so executed shall be deemed to be
an original and, all of which taken together shall constitute one and the same
Agreement. In the event that any signature is delivered by facsimile
transmission, such signature shall create a valid binding obligation of the
party executing (or on whose behalf such signature is executed) the same with
the same force and effect as if such facsimile signature were the original
thereof.

         (i)      Governing Law. All questions concerning the construction,
validity, enforcement and interpretation of this Agreement shall be governed by
and construed and enforced in accordance with the internal laws of the State of
Delaware, without regard to the principles of conflicts of law thereof. Each
party agrees that all legal proceedings concerning the interpretations,
enforcement and defense of the transactions contemplated by this Agreement
(whether brought against a party hereto or its respective affiliates, directors,
officers, shareholders, employees or agents) shall be commenced exclusively in
the state and federal courts sitting in the State of Delaware. Each party hereto
hereby irrevocably submits to the exclusive jurisdiction of the state and
federal courts sitting in the State of Delaware for the adjudication of any
dispute hereunder or in connection herewith or with any transaction contemplated
hereby or discussed herein (including with respect to the enforcement of the any
provision of this Agreement), and hereby irrevocably waives, and agrees not to
assert in any suit, action or proceeding, any claim that it is not personally
subject to the jurisdiction of any such court, that such suit, action or
proceeding is improper. Each party hereto hereby irrevocably waives personal
service of process and consents to process being served in any such suit, action
or proceeding by mailing a copy thereof via registered or certified mail or
overnight delivery (with evidence of delivery) to such party at the address in
effect for notices to it under this Agreement and agrees that such service shall
constitute good and sufficient service of process and notice thereof. Nothing
contained herein shall be deemed to limit in any way any right to serve process
in any manner permitted by law. Each party hereto hereby irrevocably waives, to
the fullest extent permitted by applicable law, any and all right to trial by
jury in any legal proceeding arising out of or relating to this Agreement or the
transactions contemplated hereby. If either party shall commence an action or
proceeding to enforce any provisions of this Agreement, then the prevailing
party in such action or proceeding shall be reimbursed by the other party for
its attorneys fees and other costs and expenses incurred with the investigation,
preparation and prosecution of such action or proceeding.

         (j)      Cumulative Remedies. The remedies provided herein are
cumulative and not exclusive of any remedies provided by law or equitable
remedies.

         (k)      Severability. If any term, provision, covenant or restriction
of this Agreement is held by a court of competent jurisdiction to be invalid,
illegal, void or unenforceable, the remainder of the terms, provisions,
covenants and restrictions set forth herein shall remain in full force and
effect and shall in no way be affected, impaired or invalidated, and the parties
hereto

                                       11
<PAGE>

shall use their best efforts to find and employ an alternative means to achieve
the same or substantially the same result as that contemplated by such term,
provision, covenant or restriction. It is hereby stipulated and declared to be
the intention of the parties that they would have executed the remaining terms,
provisions, covenants and restrictions without including any of such that may be
hereafter declared invalid, illegal, void or unenforceable.

         (l)      Headings. The headings in this Agreement are for convenience
of reference only and shall not limit or otherwise affect the meaning hereof.

                            (signature pages follow)

                                       12
<PAGE>

         IN WITNESS WHEREOF, the parties have executed this Registration Rights
Agreement as of the date first written above.

                                     NXSTAGE MEDICAL, INC.

                                     By: /s/ Jeffrey H. Burbank
                                     Name: Jeffrey H. Burbank
                                     Title: President, Chief Executive Officer

                                     DAVITA INC.

                                     By: /s/ Mark Harrison
                                     Name: Mark Harrison
                                     Title: Chief Financial Officer

<PAGE>

                                                                         ANNEX A

                              PLAN OF DISTRIBUTION

         The shares covered by this prospectus may be offered and sold from time
to time by the selling stockholder. The term "selling stockholder" includes
donees, pledgees, transferees or other successors-in-interest selling shares
received after the date of this prospectus from the selling stockholder as a
gift, pledge, distribution or other non-sale related transfer. The selling
stockholder will act independently of us in making decisions with respect to the
timing, manner and size of each sale. Such sales may be made on one or more
exchanges or in the over-the-counter market or otherwise, at prices and under
terms then prevailing or at prices related to the then current market price or
in negotiated transactions. The selling stockholder may sell its shares by one
or more of, or a combination of, the following methods:

   o     purchases by a broker-dealer as principal and resale by such
         broker-dealer for its own account pursuant to this prospectus;

   o     ordinary brokerage transactions and transactions in which the broker
         solicits purchasers;

   o     an over-the-counter distribution in accordance with the rules of The
         Nasdaq Stock Market

   o     in privately negotiated transactions;

   o     in options transactions;

   o     to or through underwriters;

   o     through dealers or agents;

   o     a block trade in which the broker or dealer so engaged will attempt to
         sell the securities as an agent but may position and resell a portion
         of the block as a principal to facilitate the transaction;

   o     through a combination of these methods; and

   o     by any other legally available means.

         In addition, any shares that qualify for sale pursuant to Rule 144 may
be sold under Rule 144 rather than pursuant to this prospectus.

         To the extent required, this prospectus may be amended or supplemented
from time to time to describe a specific plan of distribution. In connection
with the distributions of shares or otherwise, the selling stockholder may enter
into hedging transactions with broker-dealers or other financial institutions.
In connection with such transactions, broker-dealers or other financial
institutions may engage in short sales of the common stock in the course of
hedging the positions they assume with the selling stockholder. The selling
stockholder may enter into option or other transactions with broker-dealers or
other financial institutions which require the delivery to such broker-dealer or
other financial institution of shares offered by this prospectus,

<PAGE>

which shares such broker-dealer or other financial institution may resell
pursuant to this prospectus (as supplemented or amended to reflect such
transaction). The selling stockholder may also pledge shares to a broker-dealer
or other financial institution, and, upon a default, such broker-dealer or other
financial institution, may effect sales of the pledged shares pursuant to this
prospectus (as supplemented or amended to reflect such transaction).

         In effecting sales, underwriters, broker-dealers or agents engaged by
the selling stockholder may arrange for other underwriters or broker-dealers to
participate. Underwriters, broker-dealers or agents may receive commissions,
discounts or concessions from the selling stockholder in amounts to be
negotiated immediately prior to the sale. Such discounts, concessions or
commissions as to particular underwriters, broker-dealers or agents may be in
excess of those customary on the types of transactions involved.

         In offering the shares covered by this prospectus, the selling
stockholder and any broker-dealers who execute sales for the selling stockholder
may be deemed to be "underwriters" within the meaning of the Securities Act in
connection with such sales. Any profits realized by the selling stockholder and
the compensation of any broker-dealer may be deemed to be underwriting discounts
and commissions. Some of the underwriters or deemed underwriters or agents and
their associates may be customers of, engage in transactions with, and perform
services for us in the ordinary course of business.

         In order to comply with the securities laws of certain states, if
applicable, the shares must be sold in such jurisdictions only through
registered or licensed brokers or dealers. In addition, in certain states the
shares may not be sold unless they have been registered or qualified for sale in
the applicable state or an exemption from the registration or qualification
requirement is available and is complied with.

         We have advised the selling stockholder that the anti-manipulation
rules of Regulation M under the Exchange Act may apply to sales of shares in the
market and to the activities of the selling stockholder and their affiliates. In
addition, we will make copies of this prospectus available to the selling
stockholder for the purpose of satisfying the prospectus delivery requirements
of the Securities Act. The selling stockholder may indemnify any broker-dealer
that participates in transactions involving the sale of the shares against
certain liabilities, including liabilities arising under the Securities Act.

         At the time a particular offer of shares is made, if required, a
prospectus supplement will be distributed that will set forth the number of
shares being offered and the terms of the offering, including the name of any
underwriter, dealer or agent, the purchase price paid by any underwriter, any
discount, commission and other item constituting compensation, any discount,
commission or concession allowed or reallowed or paid to any dealer, and the
proposed selling price to the public.

         Notwithstanding anything to the contrary, the selling stockholder may
not sell or distribute the shares covered by this prospectus in short sales or,
without our prior written consent, which consent shall not be unreasonably
withheld, block trades.

                                       2
<PAGE>

         We will pay all expenses of the registration of the shares of common
stock pursuant to the registration rights agreement, including, without
limitation, U.S. Securities and Exchange Commission filing fees and expenses of
compliance with state securities or "blue sky" laws; provided, however, that the
selling stockholder will pay all underwriting discounts, commissions and
concessions and brokers' or agents' commissions and concessions or selling
commissions and concessions, if any. We have agreed to indemnify the selling
stockholder against certain liabilities, including certain liabilities under the
Securities Act. Underwriters, dealers and agents may be entitled to
indemnification by us and the selling stockholder against specific civil
liabilities, including liabilities under the Securities Act or to contribution
with respect to payments which the underwriters or agents may be required to
make in respect thereof, under underwriting or other agreements. The terms of
any indemnification provisions will be set forth in a prospectus supplement.

         We have agreed with the selling stockholder to keep the registration
statement of which this prospectus constitutes a part effective until the
earliest of (1) two years after the date this registration statement is declared
effective, (2) such time as all of the shares covered by this prospectus have
been publicly sold and (3) such time as all of the shares covered by this
prospectus may be sold pursuant to Rule 144(k) without volume restrictions.
Notwithstanding the foregoing obligations, we may, under specified
circumstances, suspend the use of the registration statement, or any amendment
or supplement thereto.

                                       3
<PAGE>

                                                                         ANNEX B

                        SELLING STOCKHOLDER QUESTIONNAIRE

To:      NxStage Medical, Inc.
         c/o Lia Der Marderosian, Esq.
         WilmerHale
         60 State Street
         Boston, MA 02109

Reference is made to the Stock Purchase Agreement, dated February 7, 2007 (the
"Agreement"), by and between NxStage Medical, Inc. (the "Company") and DaVita,
Inc.

Pursuant to Section 2(c) of the Agreement, the undersigned hereby furnishes to
the Company the following information for use by the Company in connection with
the preparation of the Registration Statement contemplated by Section 2(a) of
the Agreement.

         (1)      NAME AND CONTACT INFORMATION:
                                                --------------------------------
         Full legal name of record holder:
                                                --------------------------------
         Address of record holder:
                                                --------------------------------
         Social Security Number or
         Taxpayer identification number
         of record holder:
                                                --------------------------------
         Identity of beneficial owner (if
         different than record holder):
                                                --------------------------------
         Name of contact person:
                                                --------------------------------
         Telephone number of contact person:
                                                --------------------------------
         Fax number of contact person:
                                                --------------------------------
         E-mail address of contact person:
                                                --------------------------------

         (2)      BENEFICIAL OWNERSHIP OF REGISTRABLE SECURITIES:

         (a)   Number of Registrable Securities owned by Selling Stockholder:

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

         (b)   Number of Registrable Securities requested to be registered:

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

<PAGE>

         (3)      BENEFICIAL OWNERSHIP OF OTHER SECURITIES OF THE COMPANY OWNED
                  BY THE SELLING STOCKHOLDER:

         Except as set forth below in this Item (3), the undersigned is not the
         beneficial or registered owner of any securities of the Company other
         than the Registrable Securities listed above in Item (2)(a).

         Type and amount of other securities beneficially owned by the Selling
         Stockholder:

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

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

         (4)      RELATIONSHIPS WITH THE COMPANY:

         Except as set forth below, neither the undersigned nor any of its
         affiliates, officers, directors or principal equity holders (5% or
         more) has held any position or office or has had any other material
         relationship with the Company (or its predecessors or affiliates)
         during the past three years.

         State any exceptions here:

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

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

         (5)      PLAN OF DISTRIBUTION:

         Except as set forth below, the undersigned intends to distribute
         pursuant to the Registration Statement the Registrable Securities
         listed above in Item (2) in accordance with the "Plan of Distribution"
         section set forth therein:

                                       2
<PAGE>

         State any exceptions here:

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

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

    NOTE: In no event will such method(s) of distribution take the form of an
underwritten offering of the Registrable Securities without the prior agreement
of the Company.

         (6)      SELLING STOCKHOLDER AFFILIATIONS:

         (a)   Is the Selling Stockholder a registered broker-dealer?

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

         (b)   Is the Selling Stockholder an affiliate of a registered
         broker-dealer(s)? (For purposes of this response, an "affiliate" of, or
         person "affiliated" with, a specified person, is a person that
         directly, or indirectly through one or more intermediaries, controls or
         is controlled by, or is under common control with, the person
         specified.)

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

         (c)   If the answer to Item (6)(b) is yes, identify the registered
         broker-dealer(s) and describe the nature of the affiliation(s):

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

                                       3
<PAGE>

         (d)   If the answer to Item (6)(b) is yes, did the Selling Stockholder
         acquire the Registrable Securities in the ordinary course of business
         (if not, please explain)?

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

         (e)   If the answer to Item (6)(b) is yes, did the Selling Stockholder,
         at the time of purchase of the Registrable Securities, have any
         agreements, plans or understandings, directly or indirectly, with any
         person to distribute the Registrable Securities (if yes, please
         explain)?

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

    NOTE: If the Selling Stockholder is an affiliate of a broker-dealer and did
not purchase its Registrable Securities in the ordinary course of business or at
the time of the purchase had any agreements, plans or understandings, directly
or indirectly, with any person to distribute the Registrable Securities, the
Company may be required to identify the Selling Stockholder as an underwriter in
the Registration Statement, any amendments thereto and the related prospectus.

Pursuant to Section 3(c) of the Agreement, the undersigned acknowledges that the
Company may, by written notice to the undersigned, suspend or withdraw the
Registration Statement and require that the undersigned immediately cease sales
of Registrable Securities pursuant to the Registration Statement under certain
circumstances described in the Agreement. At any time that such notice has been
given, the undersigned may not sell Registrable Securities pursuant to the
Registration Statement.

The undersigned hereby acknowledges receipt of a draft of the Registration
Statement dated _____________ ___, _______ and confirms that the undersigned has
reviewed such draft including, without limitation, the sections captioned
"Selling Stockholders" and "Plan of Distribution," and confirms that, to the
best of the undersigned's knowledge, the same is true, complete and accurate in
every respect except as indicated in this Questionnaire. The undersigned hereby
further acknowledges that pursuant to Section ___ of the Agreement, the
undersigned shall indemnify the Company and each of its directors and officers
against, and hold the Company and each of its directors and officers harmless
from, any losses, claims, damages, expenses or liabilities (including reasonable
attorneys fees) to which the Company or its directors and officers may become
subject by reason of any statement or omission in the Registration Statement
made in reliance upon, or in conformity with, a written statement by the
undersigned, including the information furnished in this Questionnaire by the
undersigned.

    By signing below, the undersigned consents to the disclosure of the
information contained

                                       4
<PAGE>

herein in its answers to Items (1) through (7) above and the inclusion of such
information in the Registration Statement, any amendments thereto and the
related prospectus. The undersigned understands that such information will be
relied upon by the Company in connection with the preparation or amendment of
the Registration Statement and the related prospectus.

The undersigned has reviewed the answers to the above questions and affirms that
the same are true, complete and accurate. THE UNDERSIGNED AGREES TO NOTIFY THE
COMPANY IMMEDIATELY OF ANY CHANGES IN THE FOREGOING INFORMATION.

Dated: _________________ ___, _______   ________________________________________
                                        Signature of Record Holder
                                        (Please sign your name in exactly the
                                        same manner as the certificate(s) for
                                        the shares being registered)

                                       5

<PAGE>

                                                                       EXHIBIT A

                            INVESTOR RIGHTS AGREEMENT<PAGE>
                                                                   EXHIBIT 10.30

      As previously reported on a Current Report on Form 8-K dated December 19,
2006, on December 14, 2006, Color Kinetics Incorporated's (the Company)
Compensation Committee approved an amendment to the Company's Non-Employee
Director Compensation Plan, effective as of January 1, 2007, under which each
non-employee director will receive cash compensation of $1,000 for attending an
in-person meeting of the board of directors and cash compensation of $500 for
attending a meeting of the board of directors held by telephone conference.
Additionally, each Chairperson of the Company's Audit Committee, Compensation
Committee and Nominating Committee will receive cash compensation of $500 for
attending a meeting of his or her respective committee, whether held in-person
or by telephone conference.

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