<PAGE>
EXHIBIT 4.1


THIS NOTE AND THE SECURITIES ISSUABLE UPON EXERCISE OF THIS NOTE HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"),
OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE TRANSFERRED, SOLD,
ASSIGNED, PLEDGED, HYPOTHECATED, OFFERED OR OTHERWISE DISPOSED OF UNLESS THEY
HAVE BEEN REGISTERED UNDER THE SECURITIES ACT AND ANY APPLICABLE STATE
SECURITIES LAWS OR UNLESS AN EXEMPTION FROM REGISTRATION IS AVAILABLE.

                           NATIONAL QUALITY CARE, INC.
                             A DELAWARE CORPORATION

                    8% UNSECURED CONVERTIBLE PROMISSORY NOTE

                                       DUE

                                 MARCH 27, 2007

$ 50,000                                                          MARCH 27, 2006

         1. PAYMENT OF PRINCIPAL AND INTEREST. NATIONAL QUALITY CARE, INC., a
Delaware corporation (the "COMPANY"), hereby promises to pay to Leonardo
Berezovsky, M.D. (the "HOLDER"), at the address specified by the Holder in his
Securities Purchase Agreement (as defined below) or at such other place as the
Holder shall direct in writing, the principal sum of Fifty Thousand Dollars
($50,000), together with interest, payable in arrears on the unpaid principal
amount hereof, at the rate of eight percent (8%) PER ANNUM, in lawful money of
the United States of America, or as otherwise provided herein, which sum shall
be due and payable in one (1) installment on March 27, 2007 (the "MATURITY
DATE"). These payments shall be applied first to accrued and unpaid interest,
and thereafter to the unpaid principal amount of this Note. All references to
Dollars herein are to lawful currency of the United States of America.

         2. SECURITIES PURCHASE AGREEMENT. This Note has been issued
concurrently with a Securities Purchase Agreement (the "SECURITIES PURCHASE
AGREEMENT"), by and between the Company and the Holder, of even date herewith.

         3. EVENTS OF DEFAULT. Upon the occurrence of any of the following
specified Events of Default (each herein called an "EVENT OF DEFAULT"):

                  a. PRINCIPAL. The Company shall be in default in the due and
punctual payment of any principal amount of this Note after the date of receipt
of written notice of default and demand for payment by Holder, and any such
default shall continue unremedied for more than fifteen (15) days;


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                  b. INTEREST. The Company shall be in default in the due and
punctual payment of any interest on this Note after the date of receipt of
written notice of default and demand for payment by Holder, and any such default
shall continue unremedied for more than fifteen (15) days; or

                  c. INSOLVENCY. The Company shall suspend or discontinue its
business, or the Company shall make an assignment for the benefit of creditors
or a composition with creditors, shall file a petition in bankruptcy, shall be
adjudicated insolvent or bankrupt, shall petition or apply to any tribunal for
the appointment of any custodian, receiver, liquidator or trustee of or for it
or any substantial part of its property or assets, shall commence any
proceedings relating to it under any bankruptcy, reorganization, arrangement,
readjustment of debt, receivership, dissolution or liquidation law or statute of
any jurisdiction, whether now or hereafter in effect; or there shall be
commenced against the Company any such proceeding which shall remain undismissed
for a period of sixty (60) days or more, or any order, judgment or decree
entered or the Company shall by any act or failure to act indicate its consent
to, approval of or acquiescence in any such proceeding or in the appointment of
any custodian, receiver, liquidator or trustee of or for it or any substantial
part of its property or assets, or shall suffer any such appointment to continue
undischarged or unstayed for a period of sixty (60) days or more; or the Company
shall take any action for the purpose of effecting any of the foregoing; or any
court of competent jurisdiction shall assume jurisdiction with respect to any
such proceeding or a custodian, receiver or trustee or other officer or
representative of a court or of creditors, or any court, governmental officer or
agency shall, under color of legal authority, take and hold possession of any
substantial part of the property or assets of the Company;

then, and in any such event, and at any time thereafter, if any Event of Default
shall then be continuing, the Holder may, by written notice to the Company,
which notice shall be by certified or registered mail only, declare the
principal of and accrued interest in respect of this Note to be forthwith due
and payable, whereupon the principal of and such unpaid accrued interest in
respect of this Note shall become forthwith due and payable without presentment,
demand, protest or other notice of any kind, all of which are hereby expressly
waived by the Company.

         4. OPTIONAL CONVERSION PROVISIONS.

                  a. The Holder shall have the right, at its option, and upon
written notice of conversion, in the form attached as EXHIBIT A hereto, to
convert all, but not part, of the entire unpaid principal amount of the
obligation underlying this Note, plus all accrued interest thereon, at any time
after the date of this Note, and (subject to the satisfaction of the conditions
hereinafter described) prior to the repayment in full of the principal amount of
this Note (the "CONVERSION PERIOD"), subject to the terms and provisions of this
Note, into shares ("CONVERSION SHARES") of common stock of the Company, par
value $0.01 per share (the "COMMON STOCK"), calculated as to each conversion to
the greatest number of full shares of Common Stock, disregarding fractions, with
a cash adjustment for fractional shares as hereinafter provided, at a per share
conversion price equal to $0.48 per share (the "CONVERSION PRICE"); PROVIDED,
HOWEVER, that such right of conversion shall only be exercisable at such time as
the exercise of such


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right of conversion and the delivery of such shares of Common Stock are lawful
under federal securities laws and the securities laws of the jurisdiction of
residence of all persons to whom such shares of Common Stock are otherwise
deliverable. Notwithstanding anything to the contrary herein, the Company shall
not be obligated to deliver any certificates for any shares of Common Stock into
which this Note shall have been exercised until the delivery by the Holder to
the Company of the original of this Note. In the event the Holder shall give
notice to the Company of the Holder's exercise of such right of conversion, the
Holder shall not be entitled to withdraw the exercise of such right of
conversion without the written consent of the Company. Noteholders who do not
advise the Company of their intention to convert the Note in accordance with the
provisions hereof on or before the end of the Conversion Period shall not be
entitled to convert their Notes hereunder.

                  b. Upon such delivery of notice and surrender of this Note, as
aforesaid, the Company shall cause to be issued and to be mailed to the Holder,
as soon as practicable after the receipt by the Company of such notice and
surrender of this Note by the Holder to the Company, a certificate or
certificates for the number of full shares of Common Stock into which this Note
has been so converted upon the exercise of such conversion rights, together with
cash, as provided hereinbelow, in respect of any fractional shares of Common
Stock otherwise issuable upon such delivery and surrender. Such certificate or
certificates shall be deemed to have been issued and the Holder shall be deemed
to have become a holder of record of such shares of Common Stock as of the date
of receipt by the Company of such notice and surrender; PROVIDED, HOWEVER, that
if, at the date of such notice and surrender, the transfer books for the Common
Stock or other class of stock purchasable upon the exercise of such conversion
rights shall be closed, the certificate or certificates for the shares of Common
Stock in respect of which such conversion rights are then exercised shall be
issuable as of the date on which such books shall next be opened, and until such
date the Company shall be under no duty to deliver any certificate for such
shares of Common Stock; and PROVIDED, FURTHER, that the transfer books of
record, unless otherwise required by law, shall not be closed at any one time
for a period longer than twenty (20) days. The rights of purchase represented by
the foregoing conversion rights shall be exercisable, at the election of the
Holder, either in full or from time to time in part.

         5. NO FRACTIONAL SHARES. No fractional shares or scrip representing
fractional shares shall be issued upon the exercise of the conversion rights set
forth hereinabove. With respect to any fraction of a share called for upon the
exercise of any such conversion rights hereunder or the automatic conversion of
this Note, the Company shall issue to the Holder one whole share of Common Stock
in lieu of such fractional share.

         6. ADJUSTMENTS TO CONVERSION PRICE. The number of shares of Common
Stock issuable upon conversion of this Note shall be subject to adjustment, in
case the Company shall: (a) pay a dividend on the Common Stock in shares of
Common Stock or make a distribution in shares of Common Stock; (b) subdivide its
outstanding shares of Common Stock; (c) combine its outstanding shares of Common
Stock into a smaller number of shares of Common Stock; or (d) issue by
reclassification of its shares of stock other securities of the Company. The

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number of shares of Common Stock purchasable upon conversion of this Note
immediately prior thereto shall be adjusted so that the holder of this Note
shall be entitled to receive the kind and number of shares of Common Stock or
other securities of the Company which he would have owned or have been entitled
to receive after the happening of any of the events described above, had this
Note been converted immediately prior to the happening of such event or as of
any record date with respect thereto. An adjustment made pursuant to this
paragraph shall become effective immediately after the effective date of such
event retroactive to the record date, if any, for such event.

         7. PREPAYMENT OF NOTE. This Note shall have the following redemption
provisions:

                  a. This Note may be prepaid, at the election of the Company,
as a whole, or from time to time in part, at the price equal to the outstanding
principal of the Note and accrued interest thereon to the prepayment date, at
any time.

                  b. In case the Company shall desire to exercise the right to
prepay all or any part of the Note in accordance with its terms, it shall fix a
date for prepayment and shall mail a notice of such prepayment at least ten (10)
days prior to the date fixed for prepayment to the Holder of the Note to be
redeemed as a whole or in part at his address as the same appears on the
registry books of the Company. If mailed in the manner herein provided, the
notice shall be conclusively presumed to have been duly given, whether or not
any such Holder receives such notice. Any defect in the notice to the Holder of
any Note designated for prepayment as a whole or in part shall not affect the
validity of the proceedings for the prepayment of the Note.

         Each such notice of prepayment shall specify the date fixed for
prepayment, the prepayment price, the place where the Note is to be surrendered
for prepayment, which shall be the office of the Company, that payment will be
made upon presentation and surrender of the Note, that accrued interest to the
redemption date will be paid as specified in said notice, and that on and after
said date, interest thereon or on the portions thereof to be redeemed will cease
to accrue. If less than all the outstanding amount of the Note is to be prepaid,
the notice of prepayment shall specify the amount of the Note to be redeemed. In
case the Note is to be redeemed in part only, the notice of prepayment shall
state the portion of the principal amount thereof to be prepaid and shall state
that on and after the date fixed for prepayment, upon surrender of the Note, a
new Note in the principal amount and Maturity Date equal to the unredeemed
portion thereof will be issued.

                  c. If notice of prepayment has been mailed as above provided,
the Note or portion of the Note with respect to which such notice has been
mailed shall become due and payable on the date and at the place or places
stated in such notice, at the applicable prepayment price, together with accrued
interest to the prepayment date, and on and after said date (unless the Company
shall default in the payment of the Note at the applicable prepayment price,
together with accrued interest to said date) any interest on the Note or


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<PAGE>

portions of the Note so called for prepayment shall cease to accrue, and the
Notes and portion of the Note shall be deemed not to be outstanding hereunder
and shall not be entitled to any benefit under this Note except to receive
payment of the prepayment price, together with accrued interest to the date
fixed for prepayment. On presentation and surrender of the Note at the office of
the Company, the Note or the specified portions thereof shall be paid and
prepaid by the Company at the applicable prepayment price, together with accrued
interest, to the date fixed for prepayment.

         Upon presentation of the Note to be prepaid in part only, the Company
shall execute and deliver to the Holder, at the expense of the Company, a new
Note, of authorized denominations in aggregate principal amount and Maturity
Date equal to the unpaid portion of the Note so presented.

                  d. Notwithstanding anything to the contrary, in the event that
the Company shall deliver a notice of prepayment, the Holder shall have the
option, prior to the Company's payment of the prepayment price, but in no event
less than fifteen (15) days of the delivery of a prepayment notice by the
Company to the Holder, to convert this Note in accordance with the Optional
Conversion provisions of Section 4 of this Note.

         8. CONSOLIDATIONS AND MERGERS. In case of any consolidation of the
Company with or merger of the Company into another corporation or in case of any
sale or conveyance to another corporation of the property of the Company as an
entirety or substantially as an entirety, the Company or such successor or
purchasing corporation, as the case may be, shall execute an agreement that any
holder of this Note shall have the right thereafter, upon payment of the
Conversion Price, as the case may be, in effect immediately prior to such
action, to purchase upon conversion of this Note the kind and amount of shares
and other securities and property which he would have owned or have been
entitled to receive after the happening or such consolidation, merger, sale or
conveyance had this Note been converted immediately prior to such action. The
Company shall mail by first class mail, postage prepaid, to each holder of this
Note, notice of the execution of any such agreement. Such agreement shall
provide for adjustments, which shall be as nearly equivalent as may be
practicable to the adjustments provided for herein. The provisions of this
paragraph shall similarly apply to successive consolidations, mergers, sales or
conveyances.

         9. RESERVATION OF SHARES. There has been reserved, and the Company
shall at all times keep reserved so long as this Note remains outstanding, out
of its authorized shares of Common Stock a number of shares of Common Stock
sufficient to provide for the exercise of the rights of purchase represented by
the foregoing conversion rights. The transfer agent for any shares of the
Company's capital stock issuable upon the exercise of any of the rights of
purchase aforesaid will be irrevocably authorized and directed at all times to
reserve such number of authorized shares of Common Stock as shall be requisite
for such purpose. The Company will keep a copy of this Note on file with the
transfer agent for the Common Stock and with every subsequent transfer agent for
any shares of the Company's capital stock issuable upon the exercise of the
rights of purchase represented by the foregoing conversion rights. The Company
will supply the transfer agent with duly executed stock certificates for issue
against exercise of the foregoing conversion rights and will provide or
otherwise make available any cash which may be payable in lieu of fractional
shares as provided hereinabove. Promptly after the date of the expiration of the
foregoing conversion rights, the Company shall certify to the transfer agent the
aggregate number of shares of Common Stock previously subject to such conversion
rights, and thereafter no shares shall be subject to reservation in respect of
such conversion rights.


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<PAGE>

         10. TAXES. The Holder shall pay all taxes and charges that may be
imposed by the United States of America or any state or territory thereof
("TAXES") attributable to the initial issuance of Conversion Shares in
connection with the automatic conversion of this Note, or which may be payable
in respect of any transfer involved in the issuance of any Notes or Conversion
Shares in a name other than that of the Noteholder of record surrendered upon
the conversion of this Note, and the Company shall not be required to issue or
deliver such Conversion Shares unless or until the person or persons requesting
the issuance thereof shall have paid to the Company the amount of such Taxes or
shall have established to the satisfaction of the Company that such Taxes have
been paid.

         11. CERTAIN RESTRICTIONS ON TRANSFERABILITY.

                  a. This Note and the conversion rights set forth hereinabove
may not be sold, pledged, hypothecated, assigned, encumbered, gifted or
otherwise transferred or alienated in any manner by the Holder without delivery
of prior written notice thereof to the Board of Directors of the Company and
compliance with the provisions of this Note, and, unless such notice shall have
been so delivered and the terms of this Note shall have been so complied with,
shall not run to any assignee of the Note.

                  b. This Note has not been registered under the Securities Act
or applicable state securities laws and may not be sold, pledged or otherwise
disposed of unless it is so registered or an exemption from registration is
available and, if the Company requests, an opinion satisfactory to the Company
to such effect has been rendered by counsel. The Company is under no obligation
to register the Note or to comply with any applicable exemption from
registration. Subject to the above and the receipt of the consent of the Company
to any such transfer, the transfer of this Note may be registered by the
registered holder hereof in person or by duly authorized attorney, at the office
of the Company at the address set forth in this Note, by delivering this Note
for cancellation accompanied by delivery to the Company of a duly executed
instrument of transfer, and thereupon the Company shall execute, in the name of
the transferee or transferees, a new Note of like form for the same aggregate
principal amount.

                  c. With respect to the issue of shares of Common Stock upon
conversion of this Note and the transfer of such shares of Common Stock:

                           (i) The Holder and any transferee of the shares of
         Common Stock issuable upon the exercise of the foregoing conversion
         rights agree that, notwithstanding anything in this Note to the
         contrary, during such period as delivery of a prospectus or like
         document with respect to such Common Stock may be required by the

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<PAGE>

         securities laws of any applicable jurisdiction, no public distribution
         of such Common Stock will be made in a manner or on terms different
         from those set forth in, or without delivery of, a prospectus or other
         document then meeting the requirements of such laws. The Holder and any
         such transferee further agree that if any distribution of any of such
         Common Stock is proposed to be made to them or by them otherwise than
         by delivery of such a prospectus or other document meeting the
         requirements of the securities laws of all applicable jurisdictions,
         such action shall be taken only after submission to the Company of an
         opinion of counsel, reasonably satisfactory in form and substance to
         the Company's counsel, to the effect that the proposed distribution
         will not be in violation of such securities laws.

                           (ii) It shall be a condition to the transfer of such
         Common Stock that any transferee of such Common Stock deliver to the
         Company his or its written agreement to accept and be bound by all of
         the terms and conditions of this Note.

         12. NO STOCKHOLDER STATUS. The Holder shall not, by virtue hereof, be
entitled to any of the rights of a stockholder in the Company, either at law or
in equity; PROVIDED, HOWEVER, that in the event any certificate or certificates
representing shares of Common Stock are issued to the Holder upon exercise of
the foregoing conversion rights, then the Holder shall, for all purposes, be
deemed to have become the holder of record of such shares of Common Stock on the
date as of which such certificate or certificates were deemed issued as provided
hereinabove, irrespective of the date of delivery of such share certificate or
certificates. The rights of the Holder under this Note are limited to those
expressed herein, and the Holder, by its acceptance hereof, consents to and
agrees to be bound by and to comply with all of the provisions of this Note,
including, without limitation, all of the obligations imposed upon the Holder by
the preceding paragraph hereof.

         13. NOTICES. Any notice, demand or other communication which any party
hereto may be required or may elect to give anyone interested hereunder shall be
sufficiently given if: (a) delivered by overnight courier, and addressed, in the
case of the Company, to the address set forth on the signature page of the
Securities Purchase Agreement, and, if to the Holder, to the address set forth
on the signature page of the Securities Purchase Agreement; or (b) delivered
personally at such address; or (c) telecopied, if to the Company, at the number
set forth on the signature page of the Securities Purchase Agreement, and if to
the Holder, at the number set forth on the signature page of the Securities
Purchase Agreement, and in addition, deposited, postage prepaid, in a United
States or any other country of the Holder's residence mail box, stamped
registered or certified mail, return receipt requested and addressed in the
manner described in Section 13(a) above.

         14. ATTORNEYS' FEES. In the event that any party institutes any action
or suit to enforce this Agreement or to secure relief from any default hereunder
or breach hereof, the non-prevailing party or parties shall reimburse the
prevailing party or parties for all costs, including reasonable attorneys' fees,
incurred in connection therewith and in enforcing or collecting any judgment
rendered therein (including any appeal therefrom).


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<PAGE>

         15. CHOICE OF LAW AND FORUM. This Note shall be construed in accordance
with and be governed by the law of the State of California. Any dispute arising
under this Note, whether during the term of this Note or at any subsequent time,
shall be resolved exclusively in the courts of the State of California.

         Executed at Beverly Hills, California as of the date first written
above.

                                             "Company"

                                             NATIONAL QUALITY CARE, INC.
                                             a Delaware corporation




                                             By: /s/ RONALD LANG, M.D.
                                                 -------------------------------
                                                 Ronald Lang, M.D., Secretary


<PAGE>


                                                                       EXHIBIT A

                              NOTICE OF CONVERSION
                          (To be Executed by the Holder
                          in order to Convert the Note)

         The undersigned hereby irrevocably elects to convert $________
principal amount of the Note (defined below) into shares of common stock, par
value $0.01 per share ("COMMON STOCK"), of National Quality Care, Inc., a
Delaware corporation (the "COMPANY") according to the conditions of the "NOTE"),
as of the date written below. If securities are to be issued in the name of a
person other than the undersigned, the undersigned will pay all transfer taxes
payable with respect thereto and is delivering herewith such certificates. No
fee will be charged to the Holder for any conversion, except for transfer taxes,
if any. A copy of the Note is attached hereto (or evidence of loss, theft or
destruction thereof).

                  The undersigned hereby requests that the Company issue a
certificate or certificates for the number of shares of Common Stock set forth
below (which numbers are based on the Holder's calculation attached hereto) in
the name(s) specified immediately below or, if additional space is necessary, on
an attachment hereto:

         Name:__________________________________________________________________

         Address:_______________________________________________________________

                  The undersigned represents and warrants that all offers and
sales by the undersigned of the securities issuable to the undersigned upon
conversion of the Note shall be made pursuant to registration of the securities
under the Securities Act of 1933, as amended (the "ACT"), or pursuant to an
exemption from registration under the Act.

                  Date of Conversion:___________________________________________
                  Applicable Conversion Price: _________________________________
                  Number of Shares of Common Stock to be Issued
                  Pursuant to Conversion of the Note:___________________________
                  Name:_________________________________________________________
                  Address:______________________________________________________

                  Signature:____________________________________________________



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