<PAGE>

                                                                     EXHIBIT 4.3


                         REGISTRATION RIGHTS AGREEMENT
                         -----------------------------

     THIS REGISTRATION RIGHTS AGREEMENT (this "Agreement") is made as of March
14, 2001 (the "Effective Date"), by and between IVAX DIAGNOSTICS INC., formerly
known as B2BSTORES.COM INC., a Delaware corporation (the "Company"), and IVAX
CORPORATION, a Florida corporation ("IVAX").

                                    RECITALS

          WHEREAS, on November 21, 2000 IVAX, IVAX DIAGNOSTICS, INC.
("Diagnostics"), a Florida corporation and wholly-owned subsidiary of IVAX, and
the Company entered into a Merger Agreement whereby Diagnostics merged with and
into the Company;

          WHEREAS, pursuant to the Merger all of the issued and outstanding
shares of common stock, par value $.O1 per share of Diagnostics ("Diagnostics
Common Shares") were converted into IVAX' right to receive 20,000,000 shares of
Common Stock of the Company (the "Shares"); and

          WHEREAS, in order to induce IVAX to enter into the Merger and accept
the Shares as consideration for the Diagnostics' Common Stock, the Company and
IVAX agree that this Agreement shall govern the rights of IVAX to cause the
Company to Register the Shares.

                                   AGREEMENT

          NOW, THEREFORE, in consideration of the foregoing premises and other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties agree as follows:

     Section 1. Definitions. For purposes of this Agreement:
                -----------

     In addition to terms defined elsewhere in this Agreement, capitalized terms
used herein shall have the meanings as defined below. Such terms shall be
applicable to both the singular and plural forms of any of the terms herein
defined.

          (a) "Act" means the Securities Act of 1933, as amended.

          (b) "Common Stock" means the common stock, par value $.001 per share,
of the Company.

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

          (d) "Form S-3" means such form under the Act as in effect on the date
hereof or any Registration form under the Act subsequently adopted by the SEC
that permits inclusion or incorporation of substantial information by reference
to other documents filed by the Company with the SEC.
<PAGE>

          (e) "Holder" means any person owning Registrable Securities as of the
Effective Date or any permitted assignee thereof.

          (f) "Register", "Registered," and "Registration" refer to a
registration effected by preparing and filing a registration statement or
similar document in compliance with the Act, and the declaration or ordering of
effectiveness of such registration statement or document.

          (g) "Registrable Securities" means the Shares.

          (h) "SEC" means the Securities and Exchange Commission.

          Section 2. Company Registration. If at any time after the one year
                     --------------------
anniversary of the Effective Date the Company proposes to Register (including
for this purpose a Registration effected by the Company for shareholders other
than the Holders) any of its stock or other securities under the Act in
connection with the public offering of such securities solely for cash (other
than a Registration relating solely to the sale of securities to participants in
a Company stock plan or a Registration on any form that does not include
substantially the same information as would be required to be included in a
Registration statement covering the sale of the Registrable Securities), the
Company shall, at such time, promptly give each Holder written notice of such
Registration. Upon the written request of each Holder given within twenty (20)
days after mailing of such notice by the Company in accordance with Section
14(e), the Company shall, subject to the provisions of Section 8, include in the
Registration statement all of the Registrable Securities that each such Holder
has requested to be Registered.

     Section 3. Form of S-3 Registration. If at any time the Company shall
                ------------------------
receive from any Holder or Holders a written request or requests that the
Company effect a Registration on Form S-3 and any related qualification or
compliance with respect to all or a part of the Registrable Securities owned by
such Holder or Holders, the Company will:

          (a) Promptly give written notice of the proposed Registration, and any
related qualification or compliance, to all other Holders; and

          (b) As soon as practicable, use commercially reasonable efforts to
effect such Registration and all such qualifications and compliances as may be
so requested and as would permit or facilitate the sale and distribution of all
or such portion of such Holder's or Holders' Registrable Securities as are
specified in such request, together with all or such portion of the Registrable
Securities of any other Holder or Holders joining in such request as are
specified in a written request given to the Company within fifteen (15) days
after receipt of such written notice from the Company; provided, however, that
                                                       --------  -------
the Company shall not be obligated, pursuant to this Section 3, to effect any
such Registration, qualification or compliance (i) if Form S-3 is not available
for such offering by the Holders; (ii) if the Holders, together with the holders
of any other securities of the Company entitled to inclusion in such
Registration, propose to sell Registrable Securities and such other securities
(if any) at an aggregate price to the public (net of any underwriters' discounts
or commissions) of less than S 1,000,000; (iii) if the Company shall furnish to
the Holders a certificate
<PAGE>

signed by the Chief Executive Officer (or, if there is no Chief Executive
Officer, by the President) of the Company stating that in the good faith
judgment of the Board of Directors of the Company, it would be seriously
detrimental to the Company and its shareholders for such Form S-3 Registration
to be effected at such time, in which event the Company shall have the right to
defer the filing of the Form S-3 Registration statement for a period of not more
than one hundred twenty (120) days after receipt of the request of the Holder or
Holders under this Section 3; provided, however, that the Company shall not
                              --------  -------
utilize this right more than once in any twelve (12) month period; (iv) if the
request is received at any time before the one year anniversary of the Effective
Date; (v) in any particular jurisdiction in which the Company would be required
to qualify to do business or to execute a general consent to service of process
in effecting such Registration, qualification or compliance; or (vi) if the
Company has already effected a total of two registrations on Form S-3 for the
Holders pursuant to this Section 3.

          (c) Subject to the foregoing, the Company shall file a Registration
statement covering the Registrable Securities to be Registered as soon as
practicable after receipt of the request or requests of the Holders.

     Section 4. Obligations of the Company. Whenever required under this
                --------------------------
Agreement to effect the Registration of any Registrable Securities, the Company
shall, as expeditiously as reasonably possible:

          (a) Prepare and file with the SEC a Registration statement with
respect to such Registrable Securities and use its commercially reasonable
efforts to cause such Registration statement to become effective, and, upon the
request of the Holders of a majority of the Registrable Securities Registered
thereunder, keep such Registration statement effective until the earlier to
occur of (i) all Registrable Securities are sold under such Registraion
statement; and (ii) the date on which all Registrable Securities may be sold
pursuant to Rule 144(k) of the Act.

          (b) Prepare and file with the SEC such amendments and supplements to
such Registration statement and the prospectus used in connection with such
Registration statement as may be necessary to comply with the provisions of the
Act with respect to the disposition of all securities covered by such
Registration statement.

          (c) Furnish to the Holders such numbers of copies of a prospectus,
including a preliminary prospectus, in conformity with the requirements of the
Act, and such other documents as they may reasonably request in order to
facilitate the disposition thereunder of Registrable Securities owned by them.

          (d) Use its commercially reasonable efforts to Register and qualify
the securities covered by such Registration statement under such other
securities or blue sky laws of such jurisdictions as shall be reasonably
requested by the Holders; provided, however, that the Company shall not be
                          --------  -------
required in connection therewith or as a condition thereto to qualify to do
business or to file a general consent to service of process in any such states
or jurisdictions.

                                      -3-
<PAGE>

          (e) In the event of any underwritten public offering, enter into and
perform its obligations under an underwriting agreement, in usual and customary
form, with the managing underwriter of such offering. Each Holder participating
in such underwriting shall also enter into and perform its obligations under
such an agreement.

          (f) Notify each Holder of Registrable Securities covered by such
Registration statement at any time when a prospectus relating thereto is
required to be delivered under the Act of the happening of any event as a result
of which the prospectus included in such Registration statement, as then in
effect, includes an untrue statement of a material fact or omits to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading in light of the circumstances then existing.

          (g) Use reasonable efforts to cause all such Registrable Securities
Registered pursuant hereunder to be listed on each securities exchange or
nationally recognized quotation system on which similar securities issued by the
Company are then listed, if any.

     Section 5. Furnish Information. It shall be a condition precedent to the
                -------------------
obligations of the Company to take any action pursuant to this Agreement with
respect to the Registrable Securities of any selling Holder that such Holder
shall fumish to the Company such information regarding itself, the Registrable
Securities held by it, and the intended method of disposition of such securities
as shall be required to effect the Registration of such Holder's Registrable
Securities and represent and warrant that any such information furnished does
not contain any untrue statement of a material fact or omit to state a material
fact required to be stated in the Registration Statement.

     Section 6. Expenses of Form S-3 Registration. All expenses other than
                ---------------------------------
underwriting discounts and commissions incurred in connection with
Registrations, filings or qualifications pursuant to Section 3, including,
without limitation, all Registration, filing and qualification fees, printers'
and accounting fees, and fees and disbursements of counsel for the Company shall
be borne by the Company, but excluding underwriting discounts and commissions
relating to the Registered Securities and fees and expenses of counsel for any
selling Holder; provided, however, that the Company shall not be required to pay
                --------  -------
for any expenses of any Registration proceeding begun pursuant to Section 3 if
the Registration request is subsequently withdrawn at the request of the Holders
of a majority of the Registrable Securities to be Registered (in which case all
participating Holders shall bear such expenses; provided further, however, that
                                                ----------------  -------
if at the time of such withdrawal, the Holders have learned of a material
adverse change in the condition, business, or prospects of the Company from that
known to the Holders at the time of their request and have withdrawn the request
with reasonable promptness following disclosure by the Company of such material
adverse change, then the Holders shall not be required to pay any of such
expenses and shall retain their rights pursuant to Section 3.

     Section 7. Expenses of Company Registration. The Company shall bear and pay
                --------------------------------
all expenses incurred in connection with any Registration, filing or
qualification of Registrable

                                      -4-
<PAGE>

Securities with respect to the Registrations pursuant to Section 2 for each
Holder, including, without limitation, all Registration, filing, and
qualification fees, printers' and accounting fees relating or apportionable
thereto and the fees and disbursements of counsel for the Company, but excluding
underwriting discounts and commissions relating to Registrable Securities and
fees and expenses of counsel for any selling Holder (if other than counsel to
the Company).

     Section 8. Underwriting Requirements. In connection with any offering
                -------------------------
involving an underwriting of shares of the Company's capital stock, the Company
shall not be required to include any of the Holders' securities in such
underwriting unless they accept the terms of the underwriting as agreed upon
between the Company and the underwriters selected by it (or by other persons
entitled to select the underwriters), and then only in such quantity as the
underwriters determine in their sole discretion will not jeopardize the success
of the offering by the Company. If the total amount of securities, including
Registrable Securities, requested by shareholders to be included in such
offering exceeds the amount of securities sold other than by the Company that
the underwriters determine in their sole discretion is compatible with the
success of the offering, then the Company shall be required to include in the
offering only that number of such securities, including Registrable Securities,
which the underwriters determine in their sole discretion will not jeopardize
the success of the offering. All securities to be sold by the Company shall be
included in the offering prior to the inclusion of any Registrable Shares. The
securities to be sold by shareholders shall be apportioned pro rata among the
selling shareholders according to the total amount of securities entitled to be
included therein owned by each selling shareholder or in such other proportions
as shall mutually be agreed to by such selling shareholders. For purposes of the
preceding sentence concerning apportionment, for any selling shareholder that is
a holder of Registrable Securities and that is a partnership or corporation, the
affiliated partnerships, the partners, retired partners and shareholders of such
holder, or the estates and family members of any such partner and retired
partners and any trusts for the benefit of any the foregoing persons shall be
deemed to be a single "selling shareholder," and any pro-rata reduction with
respect to such "selling shareholder" shall be based upon the aggregate amount
of shares carrying Registrations rights owned by all entities and individuals
included in such "selling shareholder," as defined in this sentence.

     Section 9. Indemnification.
                ---------------

          (a) To the extent permitted by law, the Company will indemnify and
hold harmless each Holder, any underwriter (as defined in the Act) for such
Holder and each person, if any, who controls such Holder or underwriter within
the meaning of the Act or the Exchange Act, against any losses, claims, damages,
or liabilities (joint or several) to which they may become subject under the
Act, the Exchange Act or other federal or state securities law, insofar as such
losses, claims, damages, or liabilities (or actions in respect thereof) arise
out of or are based upon any of the following statements, omissions or
violations (collectively, a "Violation"): (i) any untrue statement or alleged
untrue statement of a material fact contained in such Registration statement,
including any preliminary prospectus or final prospectus contained therein or
any amendments or supplements thereto, (ii) the omission or alleged omission to
state therein a material fact required to be stated therein, or necessary to
make the statements therein not misleading, or (iii) any violation or alleged

                                      -5-
<PAGE>

violation by the Company of the Act, the Exchange Act, any state securities law
or any rule or regulation promulgated under the Act, the Exchange Act or any
state securities law; and the Company will pay to each such Holder, underwriter
or controlling person, as incurred, any legal or other expenses reasonably
incurred by them in connection with investigating or defending any such loss,
claim, damage, liability, or action; provided, however, that the indemnity
                                     --------  -------
agreement contained in this Section 9 shall not apply to amounts paid in
settlement of any such loss, claim, damage, liability, or action if such
settlement is effected without the consent of the Company (which consent shall
not be unreasonably withheld), nor shall the Company be liable in any such case
for any such loss, claim, damage, liability, or action to the extent that it
arises out of or is based upon a Violation that occurs in reliance upon and in
conformity with written information furnished expressly for use in connection
with such Registration by any such Holder, underwriter or controlling person.

          (b) To the extent permitted by law, each selling Holder will indemnify
and hold harmless the Company, each of its directors, each of its officers who
has signed the Registration statement, each person, if any, who controls the
Company within the meaning of the Act, any underwriter, any other shareholder
selling securities in such Registration statement and any controlling person of
any such underwriter or other shareholder, against any losses, claims, damages,
or liabilities (joint or several) to which any of the foregoing persons may
become subject, under the Act, the Exchange Act or other federal or state
securities law, insofar as such losses, claims, damages, or liabilities (or
actions in respect thereto) arise out of or are based upon any Violation, in
each case to the extent (and only to the extent) that such Violation occurs in
reliance upon and in conformity with written information furnished by such
Holder expressly for use in connection with such Registration; and each such
Holder will pay, as incurred, any legal or other expenses reasonably incurred by
any person intended to be indemnified pursuant to this Section 9, in connection
with investigating or defending any such loss, claim, damage, liability, or
action; provided, however, that the indemnity agreement contained in this
        -----------------
Section 9 shall not apply to amounts paid in settlement of any such loss, claim,
damage, liability or action if such settlement is effected without the consent
of the Holder, which consent shall not be unreasonably withheld; provided,
                                                                 --------
however, that, in no event shall any indemnity under this Section 9 exceed the
-------
net proceeds from the offering received by such Holder.

          (c) Promptly after receipt by an indemnified party under Section 9 of
notice of commencement of any action (including any governmental action), such
indemnified party will, if a claim in respect thereof is to be made against any
indemnifying party under this Section 9, delivery to the indemnifying party a
written notice of the commencement thereof and the indemnifying party shall have
the right to participate in, and, to the extent the indemnifying party so
desires, jointly with any other indemnifying party similarly noticed, to assume
the defense thereof with counsel mutually satisfactory to the parties; provided,
                                                                       --------
however, that an indemnified party (together with all other indemnified parties
-------
that maybe represented without conflict by one counsel) shall have the right to
retain one separate counsel, with the reasonable fees and expenses to be paid by
the indemnifying party, if representation of such indemnified party by the
counsel retained by the indemnifying party would be inappropriate due to actual
or potential differing interests between such indemnified party and any other
party represented by such counsel in such proceeding. The failure to deliver
written

                                      -6-
<PAGE>

notice to the indemnifying party within a reasonable time of the commencement of
any such action, if materially prejudicial to its ability to defend such action,
shall relieve such indemnifying party of any liability to be indemnified party
under this Section 9, but the omission so to deliver written notice to the
indemnifying party will not relieve it of any liability that it may have to any
indemnified party otherwise than under this Section 9.

          (d) The obligations of the Company and Holders under this Section 9
shall survive the completion of any offering of Registrable Securities in a
Registration statement under this Agreement.

     Section 10. Reports Under the Exchange Act. With a view to making available
                 ------------------------------
to the Holders the benefits of Rule 144 promulgated under the Act and any other
rule or regulation of the SEC that may at any time permit a Holder to sell
securities of the Company to the public without Registration or pursuant to a
Registration on Form S-3, the Company agrees to:

          (a) Make and keep public information available, as those terms are
understood and defined in SEC Rule 144, at all times after the effective date of
the first Registration statement filed by the Company for the offering of its
securities to the general public;

          (b) Take such action, including the voluntary Registration of its
Common Stock under Section 12 of the Exchange Act, as is necessary to enable the
Holders to utilize Form S-3 for the sale of their Registrable Securities, such
action to be taken as soon as practicable after the end of the fiscal year in
which the first Registration statement filed by the Company for the offering of
its securities to the general public is declared effective;

          (c) File with the SEC in a timely manner all reports and other
documents required of the Company under the Act and the Exchange Act; and

          (d) Furnish to any Holder, so long as the Holder owns any Registrable
Securities, forthwith upon request (i) a written statement by the Company that
it has complied with the reporting requirements of SEC Rule 144 (at any time
after ninety (90) days after the effective date of the first Registration
statement filed by the Company), the Act and the Exchange Act (at any time after
it has become subject to such reporting requirements), or that it qualifies as a
registrant whose securities may be resold pursuant to Form S-3 (at any time
after it so qualifies), (ii) a copy of the most recent annual or quarterly
report of the Company and such other reports and documents so filed by the
Company, and (iii) such other information as may be reasonably requested in
availing any Holder of any rule or regulation of the SEC that permits the
selling of any such securities without Registration or pursuant to such form.

     Section 11. Assignment of Registration Rights. The rights to cause the
                 ---------------------------------
Company to Register Registrable Securities pursuant to this Agreement may be
assigned (but only with all related obligations) by a Holder to a transferee or
assignee of such securities.

                                      -7-
<PAGE>

     Section 12. "Market Stand-Off" Agreement. IVAX hereby agrees that, during
                  ---------------------------
the period of duration (not to exceed one hundred eighty (180) days) specified
by the Company and an underwriter of common stock or other securities of the
Company, following the effective date ofthe Registration statement for a public
offering of the Company's securities filed under the Act, it shall not, to the
extent requested by the Company and such underwriter, directly or indirectly
sell, offer to sell, contract to sell (including, without limitation, any short
sale), grant any option to purchase or otherwise transfer or dispose of (other
than to donees who agree to be similarly bound) any securities of the Company
held by it at any time during such period, except common stock included in such
Registration; provided, however, that all executive officers, directors and, in
              --------  -------
the case of the Company's initial public offering, greater than five percent
(5%) stockholders of the Company enter into similar agreements. In order to
enforce the foregoing covenant, the Company may impose stoptransfer instructions
with respect to the securities of each Holder until the end of such period.

     Section 13. Termination of Registration Rights. No Holder shall be entitled
                 ----------------------------------
to exercise any right provided for in this Agreement after the earlier of (i)
five (5) years after the Effective Date, or (ii) such time at which all
Registrable Securities held by such Holder can be sold in any threemonth period
without Registration in compliance with Rule 144 of the Act.

     Section 14. Miscellaneous.
                 -------------

          (a) Successors and Assigns. Except as otherwise provided herein, the
              ----------------------
terms and conditions of this Agreement shall inure to the benefit of and be
binding upon the respective successors and assigns of the parties (including
transferees of any shares of Registrable Securities). Nothing in this Agreement,
express or implied, is intended to confer upon any party other than the parties
hereto or their respective successors and assigns any rights, remedies,
obligations, or liabilities under or by reason of this Agreement, except as
expressly provided in this Agreement.

          (b) Governing Law. This Agreement shall be governed by and construed
              -------------
under the laws of the State of Delaware, without giving effect to any choice of
law or conflict of law provision or rule (whether of the State of Delaware or
any other jurisdiction) that would cause the applications of the laws of any
jurisdiction other than the State of Delaware.

          (c) Counterparts. This Agreement may be executed in two or more
              ------------
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

          (d) Titles and Subtitles. The titles and subtitles used in this
              --------------------
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

          (e) Notices. Unless otherwise provided, any notice required or
              -------
permitted under this Agreement shall be given in writing and shall be deemed
effectively given upon personal delivery to the party to be notified or upon
delivery by confirmed facsimile transmission or nationally recognized overnight
courier services or three days following deposit with the United States Post

                                      -8-
<PAGE>

Office, by registered air mail (for international mail) or certified mail (for
domestic mail), postage prepaid and addressed to the party to be notified at the
address indicated for such party on the signature page hereof, or at such other
address as such party may designate by ten (10) days' advance written notice to
the other parties.

          (f) Expenses. If any action at law or in equity is necessary to
              --------
enforce or interpret the terms of this Agreement, the prevailing party shall be
entitled to reasonable attorneys' fees, costs and necessary disbursements in
addition to any other relief to which such party may be entitled.

          (g) Amendments and Waivers. Any term of this Agreement may be amended
              ----------------------
and the observance of any term of this Agreement may be waived (either generally
or in a particular instance and either retroactively or prospectively), only
with the written consent of the Company and the holders of at least a majority
of the Registrable Securities then outstanding.

          (h) Severability. If one or more provisions of this Agreement are held
              ------------
to be unenforceable under applicable law, such provision shall be excluded from
this Agreement, and the balance of the Agreement shall be interpreted as if such
provision were so excluded, and shall be enforceable in accordance with its
terms.

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                                      -9-
<PAGE>

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

                                    COMPANY:

                                    IVAX DIAGNOSTICS, INC., F/K/A B2BSTORES.COM,
                                    INC.


                                    By:/s/ Giorgio D'urso
                                       -------------------------------
                                       Name: Giorgio D'urso
                                       Title: President & CEO
                                       Address: 2140 North Miami Avenue
                                                Miami, Florida 33137
                                       Facsimile: (305) 324-2385

                                    IVAX:

                                    IVAX CORPORATION


                                    By:/s/ Carol J. Gillespie
                                       -------------------------------
                                       Name: Carol J. Gillespie
                                       Title: Senior Vice President
                                       Address: 4400 Biscayne Boulevard
                                                Miami, Florida 33137
                                       Facsimile:(305) 575-6049

                 SIGNATURE PAGE TO REGISTRATION RIGHTS AGREEMENT

                                       -10-