EXHIBIT 10.6

                            STOCK PURCHASE AGREEMENT

     THIS STOCK PURCHASE AGREEMENT is made as of the 14th day of July, 1987, by
and between TANOX BIOSYSTEMS, INC., a Texas corporation (the "company") , TSE
WEN CHANG, NANCY T. CHANG and ALAFI CAPITAL COMPANY, a California limited
partnership ("Alafi Capital"), SHIREEN ALAFI, JOSEPH HESKEL, TRUSTEE FOR
CHRISTOPHER ALAFI (collectively, "Alafi"), and INVITRON CORPORATION, a Delaware
corporation ("Invitron"), (collectively, Alafi Capital, Alafi, and Invitron are
referred to as the "Investors" or sometimes singly as "Investor").

     THE PARTIES HEREBY AGREE AS FOLLOWS:

     1.   PURCHASE AND SALE OF STOCK.

     1.1 SALE AND ISSUANCE OF COMMON STOCK. Subject to the terms and conditions
of this Agreement, Investors hereby severally agree to purchase, and the Company
hereby sells and issues to Investors an aggregate of 387,733 shares of the
Company's Common Stock (the "Stock") for the aggregate purchase price of
$4,000,000 paid in cash. Shares purchased severally by and sold to each of
Investors hereby are as indicated on Schedule 1.1.

     1.2 SALE OF ADDITIONAL COMMON STOCK. The Company shall have the right for a
period of sixty (60) days from the date hereof to offer up to 193,867 shares of
the Company's Common Stock (the "Additional Stock") for sale to other
prospective investors (the "Prospective Investors") at a price per share of not
less than $10.32 and on terms which, in all material respects (considered in the
aggregate), will not be more favorable to such
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Prospective Investors than the terms hereof, unless the consent of Moshe Alafi,
as the representative of Investors, is first obtained to any such more favorable
terms. At the end of such sixty (60) day period, if the Company has not
consummated the sale of the Additional Stock to one or more of the Prospective
Investors, sale of such shares of the Common Stock of the Company shall
thereafter be subject to the rights of the Investors under Section 9.

     1.3 CLOSING. The purchase and sale of the Stock has taken place at the
offices of Anderson, Harrell & Timby, P.C., 3400 MCorp Plaza, 333 Clay Street,
Houston, Texas 77002, at 9:00 A.M., July 9, 1987, or at such other time and date
as the Company and Moshe Alafi may agree, (which time and event are designated
the "Closing"). At the Closing, the Company has delivered and each of Investors
has received a certificate representing the Stock acquired by such Investor. The
Company has received from Investors a wire transfer of funds or official bank
check or checks in the aggregate amount of the purchase price. In addition, each
party has made the additional deliveries identified in Sections 5 and 6.

     2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. Except as set forth in
schedules attached hereto or otherwise disclosed in documentation delivered to
or reviewed by Investors in connection herewith, the Company, Tse Wen Chang and
Nancy T. Chang hereby represent and warrant to each Investor the matters set
forth below. Except where further qualified or the context otherwise requires,
reference in this Section 2 to the "knowledge" of the Company or matters "known
to the Company" shall mean matters actually known to the Board of Directors or

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officers of the Company. The following representations and warranties as made by
the Changs shall be deemed qualified to the extent of the actual knowledge of
each of them after due inquiry.

     2.1 ORGANIZATION GOOD STANDING AND QUALIFICATION. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of the State of Texas and has all requisite corporate power and authority to
carry on its business as now conducted. The Company is not qualified to transact
business in any other jurisdiction and its failure so to qualify will not have a
material adverse effect on its business or properties.

     2.2 CAPITALIZATION. Excluding the sales and purchases referenced in this
Agreement, the authorized capital of the Company consists of 10,000,000 shares
of common stock ("Common Stock"), of which 1,163,200 shares are issued and
outstanding and are owned of record by the persons indicated on Schedu1e 2.2 and
1,000,000 shares of preferred stock, of which no shares are issued and
outstanding. Except for (i) the Common Stock issued or to be issued under this
Agreement or to the Prospective Investors, (ii) the rights provided in or
excluded from application of Section 9 hereof, and (iii) the stock options
granted or which may be granted under the Tanox Biosystems, Inc. 1987 Stock
Option Plan, a true and correct copy of which has been delivered to the
Investors (the "Stock Option Plan"), and shares reserved for issuance
thereunder, the Company does not have any equity securities outstanding, nor are
there outstanding any options, warrants, rights, or securities convertible into
or exercisable for equity securities to be issued by the Company nor any
agreements to issue any such securities or rights.

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     2.3 SUBSIDIARIES. The Company does not own or control, directly or
indirectly, any interest in any other corporation, association, or other
business entity; provided, that this representation is not intended to apply to
any interest which may arise out of or result from license or other contractual
arrangements between the Company and any other business entity.

     2.4 AUTHORIZATION. All corporate action on the part of the Company, its
officers, directors and shareholders necessary for the authorization, execution
and delivery of this Agreement, the performance of all obligations of the
Company hereunder and the authorization, issuance (or reservation for issuance)
and delivery of the Stock being sold hereunder have been taken and this
Agreement constitutes a valid and binding obligation of the Company enforceable
in accordance with its terms, except as enforceability may be limited by
bankruptcy and similar laws or generally applicable principles of equity.

     2.5 VALID ISSUANCE OF STOCK.

     (a) The Stock purchased by Investors hereunder, as issued, sold and
delivered in accordance with the terms hereof for the consideration expressed
herein, is, or will be, duly and validly issued, fully paid and nonassessable
and, based in part upon the representations of the Investors in this Agreement
and to the Company's knowledge, is, or will be, issued in compliance with all
applicable federal and state securities laws, as the case may be; and

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          (b) All of the outstanding shares of Common Stock of the Company were
duly and validly authorized and issued, or the issuance thereof duly and validly
ratified, and are fully paid and nonassessable.

     2.6 GOVERNMENTAL CONSENTS. No consent, approval, order or authorization of,
or registration, qualification, designation, declaration or filing with, any
federal, state, local or provincial governmental authority on the part of the
Company is required in connection with the consummation of the transactions
contemplated by this Agreement, except for (a) filings which may be required
under the Securities Act of 1933, as amended, and rules and regulations
promulgated thereunder (collectively, the "Act"), and (b) the filing pursuant to
Section 25102(f) and the rules thereunder of the California Securities Law of
1968, as amended ("CSL"), or filings which may be required I under the Texas
Securities Act, as amended ("TSA").

     2.7 LITIGATION. There is no action, suit, proceeding or investigation
pending or currently threatened against the Company which questions the validity
of this Agreement or the right of the Company to enter into it, or to consummate
the transactions contemplated hereby, or which might result, either individually
or in the aggregate, in any material adverse changes in the assets, condition,
affairs or prospects of the Company, financially or otherwise, nor is the
Company aware of any basis for any of the foregoing. The Company is not a party
or subject to the provisions of any order, writ, injunction, judgment or decree
of any court or government agency or instrumentality.

     2.8 PROPRIETARY AGREEMENT. All of the Company's employees have executed a
confidentiality agreement in the form attached hereto as Exhibit 2.8. The
Company, after reasonable

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investigation, is not aware that any of its employees is in violation thereof.

     2.9 PATENTS AND TRADEMARKS. Subject to royalty and other obligations
contained in those agreements referenced on Schedule 2.9, the Company has
sufficient right, title and ownership of all patents, trademarks, service marks,
trade names, copyrights, licenses, information and proprietary rights, or
adequate licenses, rights or purchase options with respect to the foregoing,
necessary for its business as now conducted. Except as indicated by Schedule
2.9, the Company is not aware that any of its employees is obligated under any
contract (including licenses, covenants or commitments of any nature) or other
agreement, or subject to any judgment, decree or order of any court or
administrative agency, that would conflict with his obligation to use his best
efforts to promote the interests of the Company or that would conflict with the
Company's business as proposed to be conducted. To the Company's knowledge,
neither the execution nor delivery of this Agreement, nor the carrying on of the
Company's business by the employees of the Company, nor the conduct of the
Company's business as proposed will result in a breach of the terms, conditions
or provisions of, or constitute a default under, any contract, covenant or
instrument under which any of such employees is now obligated. Except for those
inventions described on Schedule 2.9, the Company does not believe it is or will
be necessary to utilize any inventions or ideas of any of its employees (or
people it currently intends to hire) made prior to their employment by the
Company.


     2.10 COMPLIANCE WITH OTHER INSTRUMENTS. The Company is not in violation or
default of any provision of its Articles of Incorporation or Bylaws or any
instrument or contract to which

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it is a party or by which it is bound or, to its knowledge, of any provision of
any federal or state judgment, writ, decree, order, statute, rule or
governmental regulation applicable to the Company. The execution, delivery and
performance of this Agreement and the consummation of the transactions
contemplated hereby will not result in any such violation or be in conflict with
or constitute, with or without the passage of time and giving of notice, either
a default under any such provision, instrument or contract or an event which
results in the creation of any lien, charge or encumbrance upon any assets of
the Company.

     2.11 AGREEMENTS; ACTION.

          (a) Except as explicitly contemplated hereby or identified on Schedule
2.11, there are no agreements, understandings or proposed transactions between
the Company and any of its officers, directors, affiliates, or any affiliate
thereof; and

          (b) Except as may be identified on Schedule 2.11, the Company has not
entered into any written agreement which provides for payments in excess of
$25,000 thereunder by the Company or any non-cancellable agreements providing
for payments in the aggregate of more than $150,000.

     2.12 DISCLOSURE. The Company has fully provided Investors with all the
information which Investors have requested for deciding whether to purchase the
Stock and all information concerning the Company which it believes is material
to enable such Investors to make such decision. Neither this Agreement nor any
other statements or certificates made or delivered in

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connection herewith contains any untrue statemant of a material fact or omits to
state a material fact necessary to make the statements herein or therein not
misleading; provided, that the foregoing does not include statements and
information contained in the preliminary draft of the Company's business plan
which has been reviewed by Investors and statements relating to potential
products, product applications, markets, sales projections or other forward
looking statements (as defined in or contemplated by Reg. 230.175 of the Act),
except that the Company and the Changs represent and warrant that the business
plan was prepared in good faith.

     2.13 REGISTRATION RIGHTS. Except as provided in Section 7 of this
Agreement, the Company has not granted or agreed to grant any registration
rights, including piggy-back rights, to any person or entity.

     2.14 CORPORATE DOCUMENTS. The Articles of Incorporation and Bylaws of the
Company are in the form last provided to the Investors.

     2.15 PROPERTIES. Except for (i) liens or encumbrances disclosed on Schedule
2.15, (ii) any lien for taxes or special assessments either not yet delinquent
or being contested in good faith by appropriate proceedings, (iii) mechanics',
materialmen's, carriers', workmen's, employees' or similar liens arising in the
ordinary course of business that do not impair in any material respect the
value, restrict the usefulness of the property, or are being contested in good
faith by appropriate proceedings, and (iv) encumbrances represented by license
or other agreements identified on schedules attached hereto or delivered to
Investors prior to Closing, the tangible and

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intangible property currently owned by the Company is free and clear of any
liens, security interests, claims, charges, options or other encumbrances. The
Company after due inquiry knows of no violation of any law, regulation or
ordinance (including without limitation laws, regulations or ordinances relating
to zoning, environmental, city planning or similar matters) relating to its
properties (owned or leased) or its business which could have a material,
adverse effect on the financial condition or operations of the business of the
Company. The Company has not received notice of any developments affecting any
of such tangible properties nor, to its knowledge, are any such developments
threatened, which might curtail the present or future use of such tangible
property for the purpose for which it was acquired or the purpose for which it
is used which could have an adverse effect on the Company. All leases under
which the Company leases any real or personal property are in good standing,
valid and effective in accordance with their respective terms.

     2.16 INSURANCE. To its knowledge, the Company is not in default with
respect to any provisions of any fire, liability, title or other form of
insurance held by it and has not failed to give any notice or present any claim
thereunder in due and timely fashion. Such policies are in amounts and upon
terms which are normal for the industry, are reasonable in light of the
Company's size and business and provide insurance for business risks normally
insured against. Such policies or binders evidencing same have been made
available for review by Investors prior to the Closing.

     2.17 TAXES. All tax returns required to be filed with respect to the
operations or assets of the Company have been correctly prepared and timely
filed or extended, and all taxes

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required to be paid in respect of the periods covered by such returns have been
paid and/or adequate reserves for the payment of all income, franchise,
property, sales, employment or other taxes payable in respect of the period
subsequent to the last of said periods have been established. No tax obligation
of the Company will arise in connection with the consummation of the
transactions contemplated hereby. The Company is not delinquent in the payment
of any assessment or governmental charge or duty the delinquency of which could
have an adverse effect on the business or operations of the Company. No
deficiencies for any tax, assessment or governmental charge or duty have been
claimed, proposed or assessed. The Company's federal income tax returns have
never been audited by federal or state authorities and, to the best of the
Company's knowledge, no such audit is currently planned.

     3. REPRESENTATIONS AND WARRANTIES OF THE INVESTORS. Investors understand
that the Stock and Additional Stock (under this Section 3, the term "Stock"
includes the Additional Stock to the extent same is intended to be acquired or
is acquired) has not been registered under the Act and applicable state laws and
that it is being offered and sold pursuant to an exemption from registration
contained in the Act and applicable state laws based in part on the
representations and warranties of Investors contained herein. Each of Investors
hereby severally represents and warrants to the Company the matters set forth
below with respect to itself.

     3.1 AUTHORIZATION. All action, corporate or otherwise, necessary for the
authorization, execution and delivery of this Agreement and performance of
Investors' obligations hereunder have been taken and this Agreement

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constitutes the valid and binding obligation, of each of the, Investors,
enforceable in accordance with its terms, except as enforceability may be
limited by bankruptcy and similar laws or generally applicable principles of
equity.

     3.2 PURCHASE ENTIRELY FOR OWN ACCOUNT. It is acquiring the Stock for its
own account and not for the benefit; of any other person (except for the
respective beneficial interests of the Alafi Capital limited partners and the
owners of Invitron) for investment purposes and not for sale or with a view
to distribution of all or any part of such Stock.

     3.3 APPLICABLE EXEMPTIONS. It understands that the Stock has not been
registered under the Act by reason of its issuance in a transaction exempt from
the registration and prospectus delivery requirements of the Act pursuant to
Section 4(2) thereof, that the Company has no present intention of registering
the Stock, that the Stock must be held by Investor indefinitely, and that
Investor must therefore bear the economic risk of such investment indefinitely,
unless a subsequent disposition thereof is registered under the Act or is exempt
from registration. Investor further understands that the Stock has not been
registered under the CSL or TSA, or other applicable state laws by reason of its
issuance in a transaction exempt from the registration requirements of such
laws, which exemptions depend upon, among other things, the bona fide nature of
Investor's investment intent expressed herein and Investors' wealth and
sophistication in making similar investments.

     3.4 ACCESS. During the negotiation of the transactions contemplated herein,
Investor and its representatives have been afforded full and free access to

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corporate books, financial statements, records, contracts, documents and other
information concerning the Company and to its offices and facilities, have been
afforded an opportunity to ask such questions of the Company's officers,
employees, agents, accountants and representatives concerning the Company's
business, operations, financial condition, assets, liabilities and other
relevant matters as they have deemed necessary or desirable, and have been given
all such information as has been requested, in order to evaluate the merits and
risks of the prospective investment contemplated herein. The foregoing, however,
does not limit or modify the representations or warranties of the Company
contained in Section 2 of this Agreement, except to the extent that any such
documents delivered to Investors reasonably disclose on the face thereof any
conflicts with such representations and warranties.

     3.5 DUE DILIQENCE. Investor and its representatives have been solely
responsible for Investor's own "due diligence" investigation of the Company and
its management and business, for Investor's own analysis of the merits and risks
of this invesuent, and for its own analysis of the fairness and desirability of
the terms of the invesuent. In taking any action or performing any role
relative to the arranging of the proposed investment, Investor has acted solely
in its own interest, and neither Investor (nor any of Investor's agents or
employees) have acted as an agent of the Company.

     3.6 CONSENTS. No consent, approval or authorization of or designation,
declaration or filing with any governmental authority on the part of Investor is
required in connection with the valid execution and delivery of this Agreement,
except for

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filings required under applicable securities and other governmental laws which
will be made and will be effective within the period required by law.

     3.7 ACCREDITED STATUS. Investor (other than Invitron) is an "accredited
investor" as that term is defined in Regulation D promulgated under the Act
and an "excluded purchaser" under Regulation 260.102.13 promulgated under the
CSL.

     3.8 INVESTMENT EXPERIENCE. Investor is an investor in securities of
companies, and/or is familiar with the risks of investment in companies, in
the development stage and acknowledges that it is able to fend for itself, can
bear for an indefinite period of time the economic risk of its investment,
including a complete loss of its investment, and has such knowledge, experience
and sophistication in financial and business matters that it is capable of
assessing the risks and merits of this investment. Investor also represents that
it has not been organized for the purpose of acquiring the Stock.

     3.9 RESTRICTED SECURITIES. Investor understands that the shares of Stock it
is purchasing are characterized as "restricted securities" under the federal
securities laws in as much as they are being acquired from the Company in a
transaction not involving a public offering and that under such laws and
applicable regulations such securities may be resold without registration under
the Act only in certain limited circumstances. In this connection, Investor
represents that it is familiar with SEC Rule 144, as presently in effect, and
understands the resale limitations imposed thereby and by the Act.

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     3.10 FURTHER LIMITATIONS ON DISPOSITION. Without in any way limiting the
representations set forth above, Investor understands and further agrees that it
cannot and will not make any disposition of all or any portion of the Stock
unless and until:

     (a) There is then in effect a registration statement under the Act covering
such proposed disposition and such disposition is made in accordance with such
registration statement; or

     (b) Investor has notified the Company of the proposed disposition and has
furnished the Company with a detailed statement of the circumstances surrounding
the proposed disposition, including why such disposition will not require
registration of such shares under the Act, and, if reasonably requested by the
Company, Investor has furnished the Company with an opinion of counsel,
reasonably satisfactory to the Company, that such disposition will not require
registration of such shares under the Act, CSL, TSA, or any applicable state
laws. It is agreed that the Company will not require opinions of counsel for
transactions made pursuant to Rule 144 except in unusual circumstances
(including circumstances where applicable state laws do not plainly except such
transaction) or for transactions made in reliance on Rule 144 (k).

     3.11 LEGENDS. It is understood that the certificates evidencing the Stock
may bear one or all of the following legends:

          (a) "These securities have not been registered under the Securities
Act of 1933 or any state securities laws.

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These securities have been acquired for investment and may not be sold, offered
for sale, pledged, hypothecated or otherwise disposed of in the absence of a
registration statement in effect with respect to the securities under such Act
and applicable state laws or an opinion of counsel satisfactory to the Company
that such registration is not required or unless sold pursuant to Rule l44 of
such Act; and

     (b) Any legend required by the laws of the State of Texas or the State of
California or required under that certain Voting Agreement dated effective of
even date herewith among the Investors and the Changs.

     4. CALIFORNIA NOTICE. THE SALE OF THE SECURITIES THAT IS THE SUBJECT OF
THIS AGREEMENT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER OF CORPORATIONS OF
THE STATE OF CALIFORNIA, AND IN THE ABSENCE OF AN EXEMPTION FROM SUCH
QUALIFICATION REQUIREMENT THE ISSUANCE OF SUCH SECURITIES OR THE PAYMENT OR
RECEIPT OF ANY PART OF THE CONSIDERATION FOR SUCH SECURITIES PRIOR TO SUCH
QUALIFICATION IS UNLAWFUL. THE RIGHTS OF ALL PARTIES TO THIS AGREEMENT ARE
EXPRESSLY CONDITIONED UPON SUCH QUALIFICATION BEING OBTAINED UNLESS IN THE
OPINION OF COUNSEL FOR THE COMPANY SUCH QUALIFICATION IS NOT REQUIRED.


     5. DELIVERIES REQUIRED BY INVESTORS AT CLOSING. In satisfaction of
Investors' conditions to Closing, Company has delivered and Investors have
received the following:

          (a) Investors have received from Anderson, Harrell & Timby, P.C.,
counsel for the Company, an opinion, dated as of the Closing, in form and
substance satisfactory to the Investors and substantially in the form of that
attached hereto as Exhibit 5(a); and

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          (b) Investors have received stock certificates representing the shares
of Stock and such other documents and agreements as they require in connection
with the Closing.

     6. DELIVERIES REQUIRED BY COMPANY AT CLOSING. In satisfaction of
Company's conditions to Closing, Investors have delivered and Company has
received the following:

          (a) Company has received from Investors (by way of wire transfer of
funds or official bank check) the aggregate purchase price of the Stock being
purchased by Investors;

          (b) Company has received from Brobeck, Phleger & Harrison, counsel for
the Investors, an opinion, dated as of the Closing, in form and substance
satisfactory to the Company and substantialy in the form of that attached
hereto as Exhibit 6(b); and

          (c) Company has received, or Investors have executed and delivered to
certain shareholders of the Company, such other documents and agreements as it
requires in connection with the Closing, including, without limitation,
confidentiality agreements and a voting agreement.

     7. REGISTRATION RIGHTS. The Company covenants and agrees to provide certain
registration rights in accordance with the terms and conditions of this
Section 7.

          7.1 DEFINITIONS. For purposes of this Section 7:

               (a) The term "register," "registered," and "registration" refer
to a registration effected by preparing and

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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;

               (b) The term "Registrable Securities" means any Common Stock of
the Company, including Common Stock issued as (or issuable upon the conversion
or exercise of any warrant, right or other security which is issued as) a
dividend or other distribution with respect to, or in exchange for or in
replacement of, such Common Stock, excluding in all cases, however, any
Registrable Securities sold by a person in a transaction in which his rights
under this Section 7 are not assignable;

               (c) The term "Holder" means any Investor, any Prospective
Investor and any other person (spouses being considered one person for purposes
hereof) provided such other person owns or has the right to acquire Registrable
Securities amounting to at least fifteen percent (15%) of the outstanding Common
Stock of the Company at any time the provisions of this Section 7 may become
exercisable or be exercised and any assignee thereof in accordance with
paragraph 7.11 hereof; and

               (d) The term "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 Securities and Exchange Commission ("SEC") which permits
inclusion or incorporation of substantial information by reference to other
documents filed by the Company with the SEC.

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          7.2 DEMAND REQISTRATION.

               (a) If the Company shall receive at any time after six (6) months
after the effective date of the first registration statement for a public
offering of securities and prior to the time the Company is eligible to utilize
Form S-3 for the sale of Registrable Securities, a written request from the
Holders of at least fifteen percent (15%) of the Registrable Securities then
outstanding that the Company file a registration statement under the Act
covering the registration of Registrable Securities then outstanding having a
market value of not less than $3,000,000, then the Company, within ten (10) days
after the receipt thereof, shall give written notice of such request to all
Holders and, subject to the limitations of subparagraph 7.2(b), shall effect the
registration under the Act of all Registrable Securities which the Holders
request to be registered as soon as reasonably possible after the mailing of
such notice by the Company, but in any event within the time required pursuant
to subparagraph 7.2(d).

               (b) If the Holders initiating the registration request hereunder
("Initiating Holders") intend to distribute the Registrable Securities covered
by their request by means of an underwriting, they shall so advise the Company
as a part of their request made pursuant to this section 7.2 and the Company
shall include such information in the written notice referred to in subparagraph
7.2(a). In such event, the right of any Holder to include his Registrable
Securities in such registration shall be conditioned upon participation in such
underwriting and the inclusion of his securities therein to the extent provided
herein. All Holders proposing to distribute their securities through such
underwriting shall (together with the Company) enter

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into an underwriting agreement in customary for with the underwriter or
underwriters selected for such Underwriting by a majority in interest of the
Initiating Holders and reasonably agreeable to the Company (the Company being
permitted to consider in connection therewith the underwriters' agreement to a
registration using incorporation of documents filed with the SEC, to the extent
permitted by applicable laws, rules and regulations, and the relative cost of
using such underwriters). Notwithstanding any other provision of this Section
7.2, if the underwriter advises the Initiating Holders in writing that marketing
factors require a limitation of the number of shares to be underwritten, then
the Initiating Holders shall so advise all Holders of Registrable Securities
which would otherwise be underwritten pursuant hereto, and the number of shares
of securities that may be included in the underwriting shall be allocated among
all Holders of Registrable Securities in proportion (as nearly as practicable)
to the amount of Registrable Securities originally requested to be included by
each in response to the written notice referred to in subparagraph 7.2(a).

               (c) The Company is obligated to effect only one (1) such
registration pursuant to this Section 7.2.

               (d) Notwithstanding the foregoing, if the Company shall furnish
to Holders requesting a registration statement pursuant to this Section 7.2, a
certificate signed by the President of the Company stating that in the good
faith judgment of the Board of Directors of the Company, it would be detrimental
to the Company and its shareholders for such registration statement to be filed
and it is therefore reasonable to defer the filing of such registration
statement, the Company shall have the

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right to defer such filing for a period of not more than one hundred twenty
(120) days after receipt of the request of the Initiating Holders; provided,
however, that the Company may not utilize this right more than once in any
twelve (12) month period. The Company shall be entitled to limit any such
registration hereunder to the same extent as permitted under subparagraph
7.10(b), subpart (6).

          7.3 COMPANY REGISTRATION. If (but without any obligation to do so) the
Company proposes to register for its own issuance or 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, the Company, each
such time, shall promptly give each Holder written notice of such registration;
provided, that such notice shall not be required, and Holders shall have no
rights hereunder, in connection with a registration relating solely to the sale
of securities to employees of the Company pursuant to any employee stock option
or stock purchase plans or a registration on any form which 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. Upon the
written request of each Holder given within twenty (20) days after mailing of
such notice by the Company in accordance with Paragraph 12.6, the Company,
subject to the provisions of Paragraph 7.6, shall cause to be registered under
the Act all of the Registrable Securities that each has requested to be
registered. The Company shall be obligated to effect only two (2) such
registrations pursuant to this Paragraph 7.3.

          7.4 FURNISH INFORMATION. It shall be a condition precedent to the
obligations of the Company to take any action pursuant to this Section 7 that
the selling Holders shall furnish

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to the Company such information regarding themselves, the Registrable Securities
held by them, and the intended method of disposition of such securities as shall
be required to effect the registration of the Registrable Securities.

          7.5 EXPENSES OF COMPANY REGISTRATION. The Company shall bear and pay
all expenses incurred in connection with any registration, filing or
qualification of Registrable Securities with respect to the registrations
pursuant to Paragraph 7.2 or 7.3 (which right may be assigned as provided in
Paragraph 7.11), including (without limitation) all registration, filing, and
qualification fees, printers' and accountinq fees relating or apportionable
thereto: provided, however, that the selling Holders shall pay the fees and
disbursements of any counsel, experts or other professionals selected by them
and: provided, further, that the fees and expenses of complying with blue sky
laws shall be borne by the selling Holders if and to the extent that the
appropriate administrative official of such state requires that such Holders
(rather than the Company) pay such fees and expenses.

          7.6 UNDERWRITING REQUIREMENTS. In connection with any offering
involving an underwriting of shares being issued by the Company, the Company
shall not be required under Paragraph 7.3 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, and then
only in such quantity as will not, in the opinion of the underwriters,
jeopardize the success of the offering by the Company. If the total amount of
Registrable Securities that all Holders thereof request to be included in such
offering exceeds the amount of such securities that the underwriters reasonably

                                      -21-
<PAGE>
believe compatible with the success of the offering or, in the initial public
offering of the Company, exceeds twenty percent (20%) of the total number of
shares proposed to be registered, then the Company shall be required to include
in the offering only that number of such securities which the underwriters
believe will not jeopardize the success of the offering or, in the initial
public offering, only that number of such securities not exceeding such twenty
percent (20%) and the Holders shall be entitled to include their respective
Registrable Securities in the offering pro rata to their ownership of same.

          7.7 DELAY OF REGISTRATION. No Holder shall have any right to obtain or
seek an injunction restraining or otherwise delaying any such registration as
the result of any controversy that might arise with respect to the
interpretation or implementation of this Section 7.

          7.8 INDEMNIFICATION. In the event any Registrable Securities are
included in a registration statement under this Section 7:

               (a) To the extent permitted by law, the Company will indemnify
and hold harmless each Holder, the officers and directors of 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
Securities Exchange Act of 1934, as amended (the "1934 Act"), against any
losses, claims, damages, or liabilities (joint or several) to which they may
become subject under the Act, the 1934 Act or other federal or state 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

                                      -22-
<PAGE>
or violations (collectively a "Violation") : (i) any untrue statement or alleged
untrue statement of 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
violation by the Company of the Act, the 1934 Act, any state securities law or
any rule or regulation promulgated under the Act, the 1934 Act or any state
securities law; and the Company will reimburse each such Holder, officer or
director, underwriter or controlling person for 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 subparagraph 7.8(a) 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 which 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 have signed the registration statement, each person, if any, who
controls the Company within the meaning of the Act, any underwriter (within the
meaning of

                                      -23-
<PAGE>
the Act) for the Company or such other Holders, any person who controls such
underwriter, and any other Holder selling securities in such registration
statement or any of its directors or officers or any person who controls such
Holder, against any losses, claims, damages, or liabilities (joint or several)
to which the Company or any such director, officer, controlling person, or
underwriter or controlling person, or other such Holder or director, officer or
controlling person may become subject, under the Act, the 1934 Act or other
federal or state 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 reimburse any legal or other expenses reasonably incurred by the
Company or any such director, officer; controlling person, underwriter or
controlling person, other Holder, officer, director, or controlling person in
connection with investigating or defending any such loss, claim, damage,
liability, or action; provided, however, that the indemnity agreement contained
in this subparagraph 7.8(b) shall not apply to amounts paid in settlement for
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; and

               (c) Promptly after receipt by an indemnified party under this
Paragraph 7.8 of notice of the 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 Paragraph 7.8,
notify the indemnifying party in writing of the commencement thereof and the

                                      -24-
<PAGE>
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 shall
have the right to retain its own counsel, with the 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 notify an
indemnifying party within a reasonable time of the commencement of any such
action, if prejudical to its ability to defend such action, shall relieve such
indemnifying party of any liability to the indemnified party under this
Paragraph 7.8, but the omission so to notify the indemnifying party will not
relieve it of any liability that it may have to any indemnified party otherwise
than under this Paragraph 7.8.

          7.9 REPORTS UNDER SECURITIES EXCHANGE ACT OF 1934. 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 use its best
efforts to:

               (a) Make and keep public information available, as those terms
are understood and defined in SEC Rule 144, at all times after ninety (90) days
after the effective date of the first registration statement filed by the
Company;

                                      -25-
<PAGE>
               (b) Take such action, including the voluntary registration of its
Common Stock under Section 12 of the 1934 Act, as is reasonable to enable the
Holders to utilize, except for the requisite financial, listing or quotation
requirements, Form S-3 for the sale of their Registrable Securities when same
becomes available, such action to be initiated as soon as reasonably 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 1934 Act; and

               (d) Furnish to any Holder, so long as the Holder owns any
Registrable Securities, forthwith (i) upon request, 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 1934 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) upon availability, 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) upon request, such other
information as may be reasonably requested in availing any Holder of any rule or
regulation of the SEC which permits the selling of any such securities without
registration or pursuant to such form.

                                      -26-
<PAGE>
The Company's obligations under this Paragraph 7.9 shall terminate at such time
as the Company may no longer be required to file reports or other documents
under the 1934 Act and will terminate as to each Holder covered hereby at such
time as such Holder shall be entitled to sell its shares under the provisions of
Rule 144(k).

          7.10 FORM S-3 REGISTRATION. In case the Company shall receive from any
Holder or Holders holding an aggregate of at least fifteen percent (15%) of the
outstanding shares of Common Stock of the Company 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 reasonably practicable, 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 within 15 days after receipt of such written notice from the Company;
provided, however, that the Company shall not be obligated to effect any such
registration, qualification or compliance, pursuant to this

                                      -27-
<PAGE>
Paragraph 7.10: (1) within 180 days of the effective date of any public offering
of securities by the Company; (2) if the Company is not qualified as a
registrant entitled to use Form S-3; (3) 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 of less than $3,000,000; (4) if the
Company shall furnish to the Holders a certificate siqned by the President of
the Company stating that in the good faith judgment of the Board of Directors of
the Company, it would be 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 120 days after receipt of the request of
the Holder or Holders under this Paragraph 7.1.0; provided, however, that the
Company shall not utilize this right more than once in any twelve (12) month
period: (5) if the Company has, within the twelve (12) month period preceding
the date for such request, already effected any registration in which each of
the Holders was entitled to register at least twenty percent (20%) of the
Registrable Securities then held by such Holder, whether pursuant to this
Paragraph 7.1.0 or otherwise; (6) 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 with respect to which such registration, qualification or
compliance is unduly burdensome: or (7) if the Company has effected at least
three (3) of such registrations pursuant to this Paragraph 7.10 for one or more
of the Holders.

                                      -28-
<PAGE>
          Subject to the foregoing, the Company will use its best efforts to
file a registration statement covering the Registrable Securities and other
securities so requested to be registered as soon as reasonably practicable after
receipt of the request or requests of the Holders. All expenses incurred in
connection with a registration requested pursuant to this Paragraph 7.1O,
including (without limitation) all registration, filing, qualification,
printers' and accounting fees and the fees and disbursements of counsel for
the selling Holder or Holders and counsel for the Company shall be borne pro
rata by the Holder or Holders participating in the Form S-3 Registration.
Registrations effected pursuant to this Paragraph 7.10 shall not be counted as
registrations effected pursuant to Paragraph 7.2 and registrations effected
pursuant to Paragraph 7.2 shall not be counted as registrations effected
pursuant to this Paragraph 7.1O.

          7.11 ASSIGNMENT OF REGISTRATION RIQHTS. The rights to cause the
Company to register Registrable Securities pursuant to this Section 7 may be
assigned by a Holder (after identification of such Holder under this Section 7
or with respect to registrations pursuant to Paragraph 7.10) to a transferee or
assignee of such securities provided (a) such assignment complies with, and such
transferee or assignee agrees in writing to comply with and be bound by all of
the terms and provisions of this Agreement, (b) the Company is, within a
reasonable time prior to such transfer, furnished with written notice of the
name and address of such transferee or assignee which notice identifies the
securities with respect to which such registration rights are being assigned and
(c) such assignment shall be effective only if immediately following such
transfer the further disposition of such securities by the transferee or
assignee is restricted under the Act.

                                      -29-
<PAGE>
          7.12 "MARKET STAND-OFF" AGREEMENT. Investors hereby agree that they
shall not, to the extent requested by the Company and an underwriter of Common
Stock (or other securities) of the Company, sell or otherwise transfer or
dispose (other) than to donees who agree to be similarly bound) of any
Registrable Securities for such period of time (not to exceed 180 days)
following the effective date of a registration statement of the Company filed
under the Act as the Company or underwriters may specify; provided, however,
that all officers and directors of the Company and all other persons with
registration rights (whether or not pursuant to this Agreement) enter into
similar agreements.

In order to enforce the foregoing covenant, the Company may impose stop-transfer
instructions with respect to the Registrable Securities of each Investor (and
the shares or securities of every other person subject to the foregoing
restriction) until the end of any such period specified.

     8. COVENANTS OF THE COMPANY.

          8.1 DELIVERY OF FINANCIAL STATEMENTS. The Company shall deliver to
each Investor:

               (a) as soon as practicable, but in any event within one hundred
twenty (120) days after the end of each fiscal year of the Company commencing
December 31, 1987, a copy of its audited report, an income statement for such
fiscal year, a balance sheet of the Company as of the end of such year, and a
schedule as to the sources and applications of funds for such year, such
year-end financial reports to be in reasonable detail,

                                      -30-
<PAGE>
prepared in accordance with generally accepted accounting principles ("gaap")
examined by and accompanied by a certificate or opinion of a nationally
recognized firm of independent certified public accountants;

               (b) commencing June 30, 1987, within sixty (60) days after the
end of each of the first three (3) quarters of each fiscal year of the Company,
an unaudited profit or loss statement for such fiscal quarter and an unaudited
balance sheet as of the end of such fiscal quarter;

               (c) as and to the extent specifically and reasonably requested
from time to time, such further financial statements, reports, information and
plans regarding the Company as the Company may prepare or have prepared for its
use; and

               (d) the financial statements called for in subparagraphs (b) and
(c) of this Paragraph 8.1 shall be accompanied by an instrument executed by the
Chief Financial Officer, Chief Executive Officer or Chief Operating Officer of
the Company and certifying that such financials were prepared in accordance with
gaap consistently applied, subject to normal year end adjustments with prior
practice for earlier periods and that such fairly present the financial
condition of the Company and its results of operation for the period specified.

          8.2 TERMINATION OF COMPANY'S COVENANTS. The covenants set forth in
Paragraph 8.1 shall terminate as to Investors and be of no further force or
effect when the Company consummates an underwritten public offering of its
securities or when the Company first becomes subject to the periodic reporting
requirements of section 15(d) of the 1934 Act, whichever event shall first
occur.

                                      -31-
<PAGE>
     9. INVESTOR'S RIGHT OF FIRST REFUSAL. Subject to the terms and conditions
specified in this Section 9, the Company hereby grants to Investors a right of
first refusal with respect to future sales by the Company of its Common Stock
(but not including the Additional Stock for a period of sixty (60) days from the
date hereof). Investors shall be entitled to apportion the right of first
refusal hereby granted among themselves in such proportions as they deem
appropriate.

          Each time the Company proposes to offer any shares of, or securities
convertible into or exercisable for, any of its Common Stock (the "Shares"),
the Company shall first make an offering of such Shares to Investors in
accordance with the following provisions:

               (a) The Company shall deliver a notice ("Notice") to Investors
stating (i) its bona fide intention to offer or issue such Shares, (ii) the
number of such Shares to be offered, and (iii) the price, if any, for which it
proposes to offer such Shares;

               (b) Within twenty (20) calendar days after receipt of the
Notice, Investors may elect to purchase or obtain, at the price and on the
terms specified in the Notice, up to that portion of such Shares which equals
the proportion that the number of shares of Common Stock issued and held by such
Investors bear to the total number of shares of Common Stock issued and held by
all shareholders of the Company (*no Investor shall be entitled to
acquire a greater percentage of the Shares than such Investor's ownership
percentage in the Company's Common Stock at such time); provided, however, that
if written notice of

*Subject to the right to apportion
 as provided above.

                                      -32-
<PAGE>
Investors election, specifying the number of Shares to be purchased by each, is
not received by the Company within such twenty-day period, Investors shall be
deemed to have waived their riqht to acquire any of such Shares;

               (c) If all such Shares which Investors are entitled to acquire
are not elected to be obtained as provided in subparagraph 9(b) hereof, the
Company may, during the l8O-day period following the expiration of the period
provided in subparagraph 9(b) hereof, offer the remaining unsubscibed Shares to
any person or persons at a price not less than, and upon terms no more favorable
to such person or persons than, those specified in the Notice; if the Company
does not enter into an agreement for the sale of the Shares within such period,
or if such agreement is not consummated with 60 days of the execution thereof,
the right provided hereunder shall be deemed to be revived and such Shares shall
not be offered unless first reoffered to Investors in accordance herewith; and

     (d) The right of first refusal in this Section 9 shall (i) terminate as to
any Investor and not be applicable to any offer or issue of the Shares to such
Investor which may be initiated by the Company after the offering and/or sale of
Shares pursuant to this Section 9 if such Investor fails in any offer under this
Section 9 to exercise * its rights to the greatest extent permitted, (ii)
terminate as to all Investors after consummation of an underwritten offering
described in (iv) below, (iii) not be applicable to shares of Common Stock
issued pursuant to any stock option or stock purchase plan to employees or
consultants of the Company provided, such plan is approved by the Company's
Board of Directors and the shares issued or issuable pursuant thereto do not
exceed twenty percent (20%) of

                                      -33-
<PAGE>
the outstanding equity securities of the Company at any time outstanding, (iv)
not be applicable to a bona fide, firmly underwritten public offering of shares
of Common Stock registered under the Act, (v) not be applicable to the issuance
of Shares in a transaction in which the Company is, in fact and irrespective of
the form of the transaction, acquiring directly or indirectly some or all of the
assets, business or equity interests of another corporation or entity, and (vi)
terminate either as of the effective date of a registration of shares of Common
Stock under the Act in which the total value of the shares registered is at
least seven million dollars ($7,000,000.00) and the price per share of the
Common Stock to be sold is based upon a total valuation of the Company of at
least thirty million dollars ($30,000,000.00) or at such time as the total value
of the Company, based upon the public trading price (whether quoted
over-the-counter or otherwise) of such shares, is at least thirty million
dollars ($30,000,000.00) .

     10. COVENANTS OF INVESTORS.

          10.1 CONFIDENTIALITY. The information provided to Investors shall be
used by the Investors or any permitted assignee of the Investors solely in
furtherance of their interests as an investor in the Company and shall be
subject to confidentiality agreements executed by Investors and any such
assignees in the form of same attached hereto as Exhibit 10.1, and executed and
delivered by the Investors to the Company at the Closing. In addition to the
obligations of confidence set forth in any such agreements, and except for the
use of any information regarding the Company contained in the public filings of
the Company under the Act or the 1934 Act or information previously reviewed by
the Company pursuant to its rights hereunder,

                                      -34-
<PAGE>
Investors agree to permit the Company to review information regarding the
Company and Investors' investment in the Company which Investors may release to
the general public or publish in any manner, including its publication in any
governmental or other filings available to the public and, as reasonable,
Investors agree to consent in good faith with Company regarding any concerns
which the company's representatives may have regarding publication of such
information. Notwithstanding anything to the contrary contained in this Section
10.1, the obligation of Invitron to consu1t with the Company prior to any
publication or filing with any governmental agency shall not be applicable if
such consultation would not be reasonably practicable under time constraints to
which Invitron may then be subject.

          10.2 LIMITATIONS ON DISPOSITION. Each of Investors agrees that it
shal1 comply fully with the limitations on disposition set forth in Paragraph
3.10 above.

          10.3 TERMINATION OF INVESTORS' COVENANTS. The covenants set forth
in Paragraphs 10.1 and 10.2 shall survive the closing, but the restrictions on
the disclosure of confidential information sha11 be coterminous with the
provisions of the confidentiality agreements pertaining thereto.

II. MISCELLANEOUS.

          II.1 SURVIVAL OF WARRANTIES. The warranties, representations and
covenants of the Company and Investors contained in or made pursuant to this
Agreement shall survive the execution and delivery of this Agreement and the
closing for a period of six (6) months (except for those covenants contained in
Sections

                                      -35-
<PAGE>
7, 8, 9, and 10 which shall continue for such period as agreed thereunder and,
in no way, shall be affected by any investigation of the subject matter thereof
made by or on behalf of the Investors.

          II.2 SUCCESSORS AND ASSIGNS. 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; provided that this Agreement may not be
transferred or assigned by Investors without the prior written consent of the
Company, which consent will not be unreasonably withheld. Nothing in this
Agreement, express or implied, is intended to confer upon any party other than
the parties hereto or their respective permitted successors and assigns any
rights, remedies, obligations, or liabilities under or by reason of this
Agreement, except as expressly provided in this Agreement.

          II.3 GOVERNING LAW. This Agreement shall be governed by and construed
under the internal laws of the State of Texas.

          1l.4 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.

          II.5 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.

          II.6 NOTICES. Any notice required or permitted under this Agreement
shall be given in writing and shall be deemed effectively given upon personal
delivery, by personal or private

                                      -36-
<PAGE>
service with appropriate record of delivery, to the party to be notified or upon
deposit with the United States Post Office, by first class mail, postage prepaid
and addressed to the party to be notified at the address indicated for such
party below, or at such other address as such party may designate by ten (1O)
days, advance written notice to the other parties :

THE COMPANY                            Tanox Biosystems, Inc..
OR THE CHANGS:                         10301 Stella Link
                                       Houston, Texas 77025
                                       Attn: Nancy T. Chang, President

ALAFI CAPITAL:                         Alafi Capital Company
                                       Post Office Box 7338
                                       Berkeley, California 94707
                                       Attn: Moshe Alafi, General Partner

ALAFI:                                 c/o Moshe Alafi
                                       6 Commodore Drive, Apt. 234C
                                       Emeryville, California 94608

INVITRON:                              Invitron Corporation
                                       4649 LeBourget Drive
                                       St. Louis, Missouri 63134
                                       Attn: Charles V. Benton, President

Notice shall be deemed effectively received (i) five (5) business days after
deposit properly addressed, with the United States Post Office, if sent first
class mail, postage prepaid, (ii) as of the date delivery is acknowledged by
appropriate record, if sent by express mail (public or private service), telex,
telegram or facsimile mail or other similar communication, or (iii) when
receipt is otherwise indicated by the receiving party to the noticing party by
correspondence, telex or other reasonable communication.

                                      -37-
<PAGE>
          II.7 FINDERS' FEE. Each party represents that it neither is nor will
be obligated for any finders' fee or commission in connection with this
transaction. Each Investor agrees to indemnify and to hold harmless the Company
from any liability for any commission or compensation in the nature of a
finders' fee (and the costs and expenses of defending against such liability or
asserted liability) for which the Investors or any of their officers, partners,
employees, or representatives are responsible.

          Each party agrees to indemnify and hold harmless the other party from
any liability for any commission or compensation in the nature of a finders' fee
(and the costs and expenses of defending against such liability or asserted
liability) for which such party is responsible.

          II.8 EXPENSES. Each party shall pay all costs and expenses that it
incurs with respect to the negotiation, execution, delivery and performance of
this Agreement.

          II.9 SEVERABILITY. If one or more provisions of this Agreement are
held to be unenforceable under applicable law, such provisions shall be excluded
from this Agreement and the balance of the Agreement shall be interpreted as if
such provision or provisions were so excluded and shall be enforceable in
accordance with its terms.

          II.10 COUNTERPARTS. This Agreement may be executed in one or more
counterparts, all of which taken together shall constitute one and the same
instrument.

                                      -38-
<PAGE>
     IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.

                                        TANOX BIOSYSTEMS, INC .

                                        By: /s/ NANCY T. CHANG
                                            Nancy T. Chang, President

                                        ALAFI CAPITAL COMPANY

                                        By: /s/ MOSHE ALAFI
                                            Moshe Alafi, General Partner

                                        /s/ SHIREEN ALAFI
                                        Shireen Alafi

                                        Joseph Heskel, Trustee for
                                        Christopher Alafi

                                        INVITRON CORPORATION

                                        By: /s/ CHARLES V. BENTON
                                            Charles V. Benton, President

                                        /s/ NANCY T. CHANG
                                        Nancy T. Chang

                                        /s/ TSE WEN CHANG
                                        Tse Wen Chang

                                      -39-
<PAGE>
IN WITNESS WHEREOF, the parties have executed this Agreement
as of the date first above written.

TANOX BIOSYSTEMS, INC.

By: /s/ NANCY T. CHANGE
Nancy T. Chang, President

ALAFI CAPITAL COMPANY

By: /s/ MOSHE ALAFI
Moshe Alafi, General Partner

/s/ SHIREEN ALAFI
Shireen Alafi

Joseph Heskel, Trustee for
Christopher Alafi

INVITRON CORPORATION

By: /s/ CHARLES V. BENTON
Charles V. Benton, President

/s/ NANCY T. CHANG
Nancy T. Chang

/s/ TSE WEN CHANG
Tse Wen Chang

                                      -39-
<PAGE>
IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.

TANOX BIOSYSTEMS, INC.

By: /s/ NANCY T. CHANG
Nancy T. Chang, President

ALAFI CAPITAL COMPANY

By:
Moshe Alafi, General Partner


Shireen Alafi

/s/ JOSEPH HESKEL
Joseph Heskel, Trustee for
Christopher Alafi


INVITRON CORPORATION

By: /s/ CHARLES V. BENTON
Charles V. Benton, President

/s/ Nancy T. Chang
Nancy T. Chang

/s/ TSE WEN CHANG
Tse Wen Chang

                                      -39-
<PAGE>
                                  SCHEDULE 1.1

INVESTOR                                            NO. OF SHARES PURCHASE PRICE
--------                                            ------------- --------------
Alafi Capital Company ........................         121,167    $1,250,004.49
Shireen Alafi ................................          24,234       250,007.10
Joseph Heskel, Trustee for Christopher Alafi .          48,466       499,993.56
Invitron Corporation .........................         193,866     1,999,994.85
<PAGE>
                                 SCHEDULE 2 .2

                                                                         NUMBER
SHAREHOLDER                                                            OF SHARES
-----------                                                            ---------
Nancy T. Chang ..........................................                520,000
Tse-Wen Chang ...........................................                450,000
William & Cecily Sun ....................................                153,200
Baylor College of Medicine ..............................                 30,000
Joseph L. Melnick .......................................                 10,000
                                                                       ---------
TOTAL ...................................................              1,163,200
<PAGE>
                                                                     EXHIBIT 2.8

                              EMPLOYMENT AGREEMENT

     THIS AGREEMENT is entered into with TANOX BIOSYSTEMS, INC., (referred to as
"Tanox"), by the undersigned employee or prospective employee (referred to as
"Employee").

     INTRODUCTION.

     Tanox is engaged in certain research, development and manufacturing
activities. Tanox also develops and manufactures equipment used in connection
with such activities.

     Employee desires to obtain or continue his (pronouns should be construed as
masculine, feminine or neuter as the context requires) employment with Tanox
and, while employed, his activities may include invention, research,
development, manufacturing, marketing and/or sale of products within the scope
of the Tanox business. This Agreement is intended to cover all of Employee's
activities as they may exist from time to time and certain of the provisions may
not apply at all times to all Employees of Tanox. Because of his position and
activities, Employee will have access to confidential and proprietary
information, trade secrets and other intellectual property of Tanox. This
Agreement will also cover Employee's activities as an employee of any subsidiary
or affiliate of Tanox should any exist from time to time.

     In consideration of the Employee's employment by Tanox or continued
employment and the compensation or increase in compensation to be paid,
Employee agrees as follows:

     1. FULL TIME RESPONSIBILITY TO TANOX. If Employee has been hired as a
full-time employee, Employee agrees that he will devote all his working time and
creative energies to the business of Tanox. Employee will perform those duties
and responsibilities assigned to him from time to time.

     2. AVOIDANCE OF CONFLICTS. Employee agrees to limit his outside activities
to personal investments and activities which do not conflict with his duties
with Tanox. Employee agrees that he will not be involved in or with, directly or
indirectly, any other business enterprise which interferes with his independent
exercise of judgement in the Company's best interest. Employee will advise Tanox
immediately of any significant financial interest held by himself or any member
of his family in a company which does business with Tanox or is a competitor.
Employee will not become involved in any significant outside business interest
without obtaining written approval of Tanox.

                                       1
<PAGE>
     3. CURRENT RELATIONSHIPS WITH OTHER BUSINESSES. Except as listed below,
Employee is not involved as an employee, director, officer or partner of, or
consultant to, any other business or institution (write none, if appropriate) :

     ___________________________________________________________________________

     ___________________________________________________________________________

     ___________________________________________________________________________

     4. INVENTIONS, PATENTS, AND OTHER INTELLECTUAL PROPERTY. Employee agrees to
inform Tanox promptly and fully of all inventions, ideas, trade secrets,
formulas, techniques, discoveries, or improvements (whether or not patentable
and whether or not reduced to writing or to practice) which he may make during
the term of his employment and for a period of one (1) year thereafter (provided
it is reasonably related to the Tanox business), whether conceived solely or
jointly by him during or outside of Tanox's normal working hours. Disclosure of
inventions and other Intellectual Property (as such term is defined below)
should be made on forms such as the attached Invention Disclosure form. Tanox
will own all right, title and interest to all Intellectual Property which is:
(1) within the scope of Tanox's past, current, or reasonably anticipated
business, which includes those areas of activities stated at the beginning of
this Agreement (all such Tanox activities and business are referred to
collectively as the "Business") ; and/or (2) related to work done for Tanox
unless a specific agreement with a client or customer provides otherwise.
Employee hereby assigns and agrees to assign to Tanox his entire right, title
and interest in all such Intellectual Property. Employee agrees to protect
Tanox's right to patent his discoveries and inventions by keeping written
records, which are witnessed and dated, concerning dates of invention, and
Employee agrees not to publish information concerning his discoveries and
inventions without prior approval from Tanox. Intellectual Property, as defined
in this Agreement, includes (but is not limited to) those matters of which
Employee has agreed above to inform Tanox and all other information of a
scientific, technical, or business nature such as know-how, manufacturing
processes, chemical processes, product designs, writings and other works of
authorship, theses, books, computer programs, lectures, illustrations,
photographs, sales, profits and other financial figures, marketing plans,
business methods, customer lists, and the like, which is reasonably related to
the Business, including that of Tanox's affiliates or subsidiaries, if any.

     5. BIOLOGICAL MATERIALS. Because of the importance of biological materials
developed by Tanox to the success of its business, Employee specifically
acknowledges that all biological

                                       2
<PAGE>
materials created, discovered, or isolated by Employee within the scope of his
employment are a part of the Intellectual Property and are the property of
Tanox. Biological materials include (but are not limited to) cells, cell lines
or multicellular organisms, Microorganisms, transfected or transformed cells or
cell lines, fused cells or cell lines (e.g. hybridoma cells) products of such
cells or cell lines (e.g. natural or recombinant proteins such as enzymes,
hormones, biological regulatory factors, antigens and immunoglobulins), nucleic
acid vectors and recombinant DNA plasmids and clones harboring genes or DNA for
biological products. Employee agrees that during his employment by Tanox and
thereafter, he will not take for his own use or transfer or release or cause to
be transferred or released to any other person or entity, any of the biological
materials. Employee may do so only with the authority and permission of Tanox.

     6. COPYRIGHTS. Employee agrees that any copyrightable material generated by
him while employed by Tanox shall be presumed a "work made for hire" and shall
vest in Tanox as the "AUTHOR" thereof. However, if any of the material is not
properly considered a "work made for hire," Employee agrees, if requested by
Tanox, to take out copyrights on Tanox's time and under direction of Tanox's
attorneys and to assign such copyrights to Tanox or its clients or customers.
Employee further agrees that rights to all royalties resulting from such
copyrights will be the property of Tanox or its clients. Regardless of the
above, it is understood, however, that copyrights in material resulting from
professional activities of a general nature not relating to the Business or
resulting from a specific assignment from Tanox or its clients or customers are
Employee's own property. Employee agrees, however, to submit all such material
to Tanox for review prior to public release so that Tanox may insure that the
Employee's obligations of confidentiality are being met.

     7. PATENT FILINGS. If requested to do so by Tanox, Employee agrees to do
whatever is necessary, on Tanox's time and under direction of Tanox's attorneys,
to obtain patents in any country and to assign to Tanox all patents and patent
applications, whether U.S. or foreign, relating to them, before or after
leaving Tanox's employment. It is understood that the cost of making such
assignments and procuring patents shall be paid by Tanox or Tanox's clients or
customers. Employee further agrees that rights to all royalties resulting from
such patents will be the property of Tanox or its clients or customers.

     8. CURRENT INVENTIONS. Except as set forth on the Invention Disclosure form
attached, Employee agrees that he does not have an interest in any inventions,
discoveries, improvements abstracts, articles, papers or other Intellectual
Property which is not already patented or copyrighted, which were made or
conceived of prior to employment with Tanox.

                                       3
<PAGE>
     9. NON-DISCLOSURE OF CONFIDENTIAL MATTERS. Employee acknowledges that he
may have access to confidential information, concerning Tanox and its
subsidiaries and affiliates, if any, and concerning its clients and customers,
which may include (but not be limited to) the Intellectual Property, books and
records relating to operations, finance, accounting, sales, personnel and
management; policies and matters relating particularly to operations such as
customer names, addresses and price lists, customer service requirements, costs
of providing service and equipment, operating and maintenance costs and pricing
matters. The Employee also recognizes that a portion of the Business is
dependent upon a large number of trade secrets, including secret techniques,
methods, processes, data and the like. The protection of these trade secrets
and confidential information against unauthorized disclosure or use is of
critical importance to Tanox, and the Employee therefore agrees that he will not
at any time, either while employed by Tanox or afterwards, make any independent
use of, or disclose to any other person or organization, except as authorized by
Tanox, any of the trade secrets or confidential information of Tanox. Employee
acknowledges that confidential matters and trade secrets include information not
generally known by or available to the public about or belonging to Tanox and
also includes proprietary information belonging to other companies to whom Tanox
may have an obligation to maintain information in confidence. Employee agrees
that authorization for public disclosure may only be obtained through Tanox's
written consent.

     Employee, in addition, agrees not to disclose to Tanox, or induce Tanox to
use, any trade secrets or confidential information of any of the Employee's
previous employers. Employee represents that he is free to disclose all
information he may now possess and bring with him, except as noted below:

________________________________________________________________________________

________________________________________________________________________________

________________________________________________________________________________

     10. COMPETITIVE ACTIVITIES.

          (a) SCIENTIFIC/TECHNICAL. If employee has been or is employed by Tanox
in a scientific, technical or other non-sales capacity, as an independent
covenant, Employee further agrees to refrain, both during his employment and
upon termination of his employment for any reason, for three (3) years after his
termination, from becoming involved in any way in any business competitive
with the Business, whether as an employee, consultant, partner, proprietor or
in any other capacity, except as a shareholder owning less than five percent
(5%) of the shares of a

                                       4
<PAGE>
corporation whose shares are publicly traded on a stock exchange or in the
over-the-counter market or unless permission of Tanox is obtained. Employee
understands that, because of the nature of his employment activities for Tanox,
geographical limitation as to any activities by him after termination which
would directly compete with the Business must include Tanox's reasonable market
area to be effective and to protect its interests. Therefore, the foregoing
restriction on competitive activities shall apply to the United States of
America, such geographical restriction being agreed by Employee to be
reasonable.

          (b) SALES/MARKETING. If Employee has been or is employed by Tanox in
whole or in part in a sales capacity, as an independent covenant, Employee
further agrees, in the event of the termination of his employment with Tanox for
any reason, to refrain, for two (2) years thereafter, from contacting and/or
soliciting, directly or indirectly, on behalf of himself or for others, for any
purpose competitive with the Business, (a) any accounts, contracts, references
or referrals of companies or persons which are potential customers or clients
of, or investors in, Tanox, or (b) any accounts, contracts, references or refer-
rals of companies, persons or other potential customers, clients or investors
who have contacted Tanox regarding its Business.

          (c) INJUNCTION. If the provisions of this Paragraph 10 are violated,
in whole or in part, Tanox shall be entitled, upon application to any court of
proper jurisdiction, to restrain and enjoin the Employee from such violation
without limiting any other remedies Tanox may have at law or in equity. Further,
in the event that the provisions of Paragraph 10 should ever be determined to
exceed the time, geographic or occupational limitations permitted by the
applicable laws, the Employee and Tanox agree that such provisions shall be and
are reformed to the maximum time, geographic or occupational limitations
permitted by the applicable laws.

     II. IMPROPER PAYMENTS. Employee represents and agrees that he will make no
payments of any kind which violate any policy of Tanox or any applicable statute
or rule, regulation or order of any government or municipality, foreign or
domestic. Employee will be responsible for any liabilities, obligations, claims,
penalties, fines or losses resulting from any unauthorized or unlawful acts of
Employee or from any violations by Employee of any such policies, laws or
regulations, whether willful or not. The provisions of this Paragraph 11 will
continue after termination of this Agreement.

     12. EMPLOYEE POLICIES. Employee agrees that he will read and gain an
understanding of all policies and procedures which may be contained from time to
time in any employee policy and procedures manual and/or safety handbook
applicable to Tanox. Employee understands that such policies and procedures,
including

                                       5
<PAGE>
any revisions or supplements to same from time to time, are, or will be,
applicable to the Employee in the performance of his duties and job performance
for Tanox and he agrees to strictly observe all of such policies and procedures.

     13. TERMINATION. Upon the termination of his employment for any reason,
Employee will promptly turn over to Tanox all manuals, handbooks, programs,
models, prototypes, notes, memorandums, notebooks, drawings, records, documents,
and the like, and all copies of same, in his possession or under his control,
whether prepared by Employee or others, relating to Intellectual Property and/or
the Business. Employee acknowledges that all such items are the sole property of
Tanox.

     14. BINDING EFFECT. Employee agrees that this Agreement shall be binding
upon him irrespective of the duration of his employment by Tanox, the reasons
for the cessation of his employment, or the amount of his wages and/or salary.
Employee acknowledges that his wages and/or salary shall be established from
time to time by Tanox. Modification or variation of this Agreement must be
accomplished by a subsequent written agreement signed by Tanox to be valid.
Tanox may assign this Agreement in its entirety to a successor corporation
carrying on all or a substantial part of the business of Tanox.

     15. SEVERABILITY. Should any provision or any part of any provisions of
this Agreement be held to be void or unenforceable, the validity of the
remaining parts or provisions shall not be affected by such holding.

     EXECUTED this ___ day of ______, 198__, to be effective upon employment.

                                                 -------------------------------
                                                 Employee's Name (Type or Print)

                                                 -------------------------------
                                                 Employee's Signature

Acknowledged and agreed:

TANOX BIOSYSTEMS, INC.

By:

Its:

                                       6
<PAGE>
                             TANOX BIOSYSTEMS, IRC.
                              Invention Disclosure

INVENTOR(S)

     Name _______________________________ Name _______________________________

     Name _______________________________ Name _______________________________

DESCRIPTIVE TITLE OF INVENTION:
______________________________________________________________________________

______________________________________________________________________________

DESCRIPTION OF INVENTION:
Please provide a concise description of your invention, including an explanation
of the nature, purpose and operation of the invention; a summary of results
achieved; features believed to be novel; further experimental work planned; and
any additional information which you believe might be helpful in deciding
whether a patent application should be filed. ADDITIONAL SHEETS CAN BE USED, but
each must be attached to this form and EACH MUST BE SIGNED AND WITNESSED:

______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

                                       7
<PAGE>
CONCEPTION
Date of which you conceived (thought of) the invention.
______________________________________________________________________________

NOTE PRINTED PUBLICATIONS, ABSTRACTS, ORAL PRESENTATIONS OR OTHER DIVULGATIONS
MAY RESULT IN IMMEDIATE LOSS OF RIGHTS TO OBTAIN PATENT PROTECTION.

     PLEASE ATTACH A COPY OF ANY PAPER, ABSTRACT OR OTHER PRINTED PUBLICATION,
INCLUDING A ROUGH DRAFT IF PUBLICATION IS NOT YET IN FINAL FORM.

     A SALE OR OFFER TO SELL MAY RESULT IN IMMEDIATE LOSS OF RIGHTS TO OBTAIN
PATENT PROTECTION.

PUBLICATION INFORMATION
Please list any papers, abstracts, etc. describing the invention which have been
published or submitted for publication. Include the title, journal and date or
estimated date of publication.
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

Please indicate whether an oral presentation (including slide or poster
presentation) of the invention or a sale or offer to sell the invention has been
or will be made and, to whom.

______________________________________________________________________________
__________________________________________________________Date________________

FINANCIAL SUPPORT

Please designate all sources of funding for the invention other
than Tanox Biosystems:________________________________________________________
______________________________________________________________________________


COMMERCIAL POTENTIAL OF THIS INVENTION
Please provide your assessment of the commercial uses of the invention:
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________

INVENTOR(S) SIGNATURE (S)                    READ, UNDERSTOOD AND WITNESSED
__________________________ ____              _________________________ ____
                           Date                                        Date

__________________________ ____              _________________________ ____
                           Date                                        Date

__________________________ ____              _________________________ ____
                           Date                                        Date
                                       8
<PAGE>
                                 SCHEDULE 2.9

AGREEMENT BETWEEN TANOX AND                                  EFFECTIVE DATE
---------------------------                                 -----------------
Tse-Wen Chang                                               January 1, 1987
Baylor College of Medicine                                  January 1, 1987
Baylor College of Medicine                                  February 25, 1987
<PAGE>
                                 SCHEDULE 2.11

AGREEMENT BETWEEN TANOX AND        TYPE OF AGREEMENT         AMOUNT
---------------------------        -----------------        -------
Tse-Wen Chang, Ph.D.               R & D Consulting         $12,000

Joseph IN Melnick, Ph.D.           Scientific Advisor        10,000
                                                             shares

Main Link Business Park Assoc.     Building lease           $490,380

Sorin Biomedica, S.p.A.            Peptide Manufacture      $60,000
<PAGE>
                                  SCHEDULE 2.l5

Lien dated June 4, 1987 in the amount of $25,079 for HVAC
     sub-contracting threatened but not FILED. Said lien
     affidavit INCORRECTLY identifies Tanox as property
     owner.
<PAGE>
                                 July ___, 1987

Alafi Capita1 Company
Attn: Mr. Moshe Alafi
Ms. Shireen Alafi
Mr. Joseph Heskel, Trustee
Post Office Box 7338
Berkley, California 94707

Invitron Corporation
Attn: Mr. Charles V. Benton, President
4649 LeBourget Drive
St. Louis, Missouri 63134

      Re: Purchase of 387,733 shares of Common Stock from Tanox Biosystems, Inc.

Gentlemen:

     We have acted as counsel to Tanox Biosystems, Inc., a Texas corporation
(the "Company"), and to Tse Wen Chang and Nancy T. Chang (the "Changs") in
connection with the sale by the Company of 387,733 shares of common stock, $0.01
par value per share, in the aggregate (the "Stock"), to Alafi Capital Company,
Shireen Alafi, Mr. Joseph Heskel, Trustee for Christopher Alafi, and Invitron
Corporation (collectively, the "Purchasers"). This opinion is being provided to
you pursuant to the provisions of that certain Stock Purchase Agreement dated
effective July 9, 1987 (the "Agreement") between the Company and Purchasers.
Unless otherwise required by the context thereof or separately defined herein,
all capitalized terms used in this letter have the meanings set forth in the
Agreement.

     Before rendering the opinions set forth below, we examined certain
certificates of public officials, Restated Articles of Incorporation and Bylaws
of the Company, the Agreement, that certain Voting Agreement dated effective
July 9, 1987 (the
<PAGE>
Alafi Capital Company
Invitron Corporation
July __, 1987
Page 2
----------------------------------

"Voting Agreement") and such corporate and other available documents as we
believed to be necessary for purposes of this opinion. In rendering this
opinion, we have assumed the genuineness of all signatures, the authenticity of
all documents submitted to us as originals, and the conformity to original
documents of all documents submitted to us as certified or photostatic copies.
We have also assumed that such documents have been duly executed and delivered
by all parties thereto other than the Company and the Changs and that there
exists no facts arising out of or resulting from actions of such other parties
which would impair in any manner the validity, binding effect, or enforceability
of such documents against such other parties, as the case may be.

     In connection with rendering this opinion, we call your attention to the
fact that our firm represents the Company only in connection with specific
requests of the Company from time to time and that there may exist matters of a
legal nature involving the Company with respect to which we have no knowledge.
Nothing in this opinion is intended either to imply knowledge of matters or
documents or the contents thereof of which we have no actual knowledge or to
imply what we have made any independent factual investigations of such matters.

     We have discussed with representatives of the Company certain factual
matters relative to our opinion. With respect to the accuracy of any factual
matters relative to this opinion, we have relied upon such discussions, upon the
representations of the Company contained in the Agreement, and upon certain
certificates of government officials. We have also relied upon discussions with
representatives of the Company to assess materiality with respect to any matters
covered by our opinion which are so qualified. This opinion is further qualified
by any exceptions, exclusions or other matters contained in the Agreement, the
Voting Agreement, or set forth on exhibits or schedules attached to or
incorporated as a part of the Agreement.

     We are licensed to practice only in the State of Texas and we have limited
our opinion solely to the laws of the State of Texas and the federal laws of the
United States. We express no opinions with regard to any matter which is covered
by the laws of any other state or jurisdiction.

     Based upon and subject to the foregoing, we are of the opinion that:
<PAGE>
Alafi Capital Company
Invitron Corporation
July __, 1987
Page 3
----------------------------------

     1. The Company is a corporation duly organized, validly existing, and in
good standing under the laws of the State of Texas and has the corporate power
and authority to carry on its business as now conducted. The Company is not
qualified to transact business in any other jurisdiction as a foreign
corporation. We do not know of any activities of the Company which, with
reasonable certainty, would give rise to an obligation of the Company to qualify
in any other jurisdiction.

     2. The authorized capital of the Company as established by the Restated
Articles of Incorporation, filed with the Secretary of State on
_________________, 1987, consists of ten million (10,000,000) shares of Common
Stock and one million (1,000,000) shares of Preferred Stock. To our knowledge,
there were outstanding immediately prior to the sale of the Stock to Purchasers,
one million one hundred sixty-three thousand two hundred (1,163,200) shares of
common stock. Two hundred thousand (200,000) shares have been reserved for
issuance by the Company pursuant to the Tanox Biosystems, Inc. 1987 Stock Option
Plan.

     3. To our knowledge, the Company does not own, of record or beneficially,
an equity interest in any other entity.

     4. The Agreement has been duly executed by the Company and the Changs and
constitutes a valid and binding obligation of the Company and the Changs,
enforceable against each of the Company and the Changs in accordance with the
terms thereof, except to the extent that enforcement thereof may be limited by
applicable bankruptcy, insolvency, moratorium, and similar laws affecting
creditors' rights generally, by the exercise of judicial discretion under
generally applicable principles of equity or by the exercise of regulatory or
judicial discretion under applicable securities laws.

     5. The Stock to be sold by the Company to Purchasers in accordance with the
Agreement has been duly authorized, and when delivered against payment for such
Stock, will be validly issued, fully paid and nonassessable. We do not know of
any matters relative to the status or actions of the Company in connection
<PAGE>
Alafi Capital Company
Invitron Corporation
July __, 1987
Page 4
----------------------------------

with the sale and issuance of the Stock pursuant to the Agreement which would
eliminate the availability of exemptions from the registration or other
qualification requirements of applicable state and federal securities laws,
respectively, upon which the Company may rely.

     6. To our knowledge, no consent, approval, order or authorization, or
registration, qualification, designation, declaration or filing with, any
federal, state, or local governmental authorition the part of the Company is
legally required for the valid execution, delivery, and performance of the
Agreement by the Company, except for such filings as may be required under
applicable securities laws to claim the benefit of certain available exemptions
from registration or other required qualification of securities.

     7. To our knowledge, there is no action, suit, proceeding, or investigation
pending, or currently threatened, against the Company which questions the
validity of the Agreement or the right of the Company to consummate the sale of
the Stock to Purchasers, or which might result, either individually or in the
aggregate, in any material adverse change in the properties, financial condition
or operations of the Company, and the Company is not a party or subject to the
provisions of any order, writ, injunction, judgment or decree of any court or
governmental agency or instrumentality.

     8. The sale of the Stock pursuant to the Agreement does not violate and is
not in conflict with any of the provisions of the Restated Articles of
Incorporation or Bylaws, and, to our knowledge, does not result in a default
under or violation of any agreement or instrument to which the Company is a
party or by which the Company is bound, which breach or default would have a
material adverse effect on the properties, financial condition, or operations of
the Company.

     9. The Voting Agreement has been duly executed and delivered by the Changs
and constitutes a valid and binding obligation of the Changs. Under Article
2.30B of the Texas Business Corporation Act, upon deposit of a counterpart of a
voting agreement with the corporation at its principal office and endorsement
<PAGE>
Alafi Capital Company
Invitron Corporation
July __, 1987
Page 5
----------------------------------

     upon the certificate representing shares subject to such voting agreement
     of a statement that the shares represented by the certificate are subject
     to the provisions of a voting agreement, a counterpart of which has been
     deposited with the corporation at its principal office, such voting
     agreement shall be specifically enforceable in accordance with the
     principles of equity.

     The opinions expressed herein and the statements herein made are solely
for the benefit of the addressees and may not be relied upon any other person
without our prior written consent.

                                             ANDERSON, HARRELL & TIMBY, P.C.
                                             By:____________________________
                                                     David Anderson
<PAGE>
EXHIBIT 6(B)

                                  July __, 1987
Tanox Biosystems, Inc.
10301 Stella Link
Houston, Texas 77025

          Re:  Stock Purchase Agreement with Invitron Corporation, Alafi Capital
               Company, Shireen Alafi and Joseph Heskel, as Trustee for
               Christopher Alafi

Gentlemen:

     We have acted as counsel for Invitron Corporation, Alafi Capital Company
("ACC") , Shireen Alafi and Joseph Heskel, as Trustee for Christopher Alafi
(collectively the "Investors") in connection with the issuance and sale by you
of an aggregate of 387,733 shares of common stock, $0.01 par value per share
(the "Stock") pursuant to a Stock Purchase Agreement dated as of July __, 1987
among the Investors, Tse Wen Chang, Nancy T. Chang and Tanox Biosystems, Inc.
(the "Agreement") .

     As used in this opinion, the capitalized terms shall have the same meaning
as ascribed to them in the Agreement unless the context otherwise requires. In
connection with this opinion we have reviewed the Agreement, the Voting
Agreement, the partnership agreement, as amended, of
<PAGE>
Tanox Biosystems, Inc.
July __,1987                                                                  2.

ACC, and limited partnership certificate of ACC, the trust agreement for
Chistopher Alafi, the Certificate of Incorporation and Bylaws of Invitron
Corporation and such other available documents as we believed necessary for this
opinion. In rendering this opinion, we have assumed the genuineness of all
signatures, the authenticity of all documents submitted to us as originals, and
the conformity to original documents submitted to us as certified or photo-
static copies. We have also assumed that such documents have been duly executed
and delivered by all parties thereto other than the Investors and that there
exist no facts arising out of or resulting from actions of such other parties
which would impair in any manner the validity, binding effect, or enforceability
of such documents against such other parties, as the case may be.

     While we are general counsel to ACC, there may exist matters of a legal
nature involving ACC with respect to which we may have no knowledge. We are not
general counsel to Invitron Corporation and represent it only in connection with
specific matters referred to us. Nothing contained herein is intended either to
imply knowledge of matters or documents or the contents thereof of which we have
no actual knowledge or to imply that we have made any independent factual
investigation of such matters.
<PAGE>
Tanox Biosystems, Inc.
July __,1987                                                                  3.

     The opinions expressed herein are limited to the 1aws of the State of
California and the federal laws of the United States. No opinion is expressed as
to the law of any other jurisdiction.

     Based upon and subject to the foregoing, in accordance with the provisions
of Section 6(b) of the Agreement, we hereby advise you of our opinion that:

     (a) ACC is a limited partnership duly organized, validly existing and in
good standing under the laws of the State of California.

     (b) Invitron Corporation is a corporation duly organized, validly existing,
and in good standing under the laws of the State of Delaware.

     (c) The Agreement has been duly executed by each of the Investors and
constitutes a legal and valid binding obligation of each of them enforceable
against each in accordance with the terms thereof, except as rights to
indemnity may be limited by applicable laws and subject to laws of bankruptcy,
insolvency and other laws of general application affecting rights and remedies
of creditors, and further subject to general principles of equity (regardless
of whether such enforcement is considered in a proceeding in equity or at
law).
<PAGE>
Tanox Biosystems, Inc.
July __,1987                                                                  4.

     (d) We are not aware of any matters relative to the status or action of
the Investors, or any of them, in connection with the purchase and receipt of
the Stock pursuant to the Agreement which would eliminate the availability
of exemptions from the registration or other qualification requirements of the
Securities Act of 1933, as amended, or the California Corporate Securities Law
of 1968, as amended, respectively, upon which the Company may rely.

     (e) To our knowledge, no consent, approval, order or authorization, or
registration, qualification, designation, declaration or filing with, any
federal, state, or local governmental authority on the part of the Investors, or
any of them, is legally required for the valid execution, delivery, and
performance of the Agreement by each of the the Investors, except for such
filings as may be required under applicable securities laws to claim the benefit
of certain available exemptions from registration or other required
qualification of securities.

     (f) The purchase of the Stock pursuant to the Agreement does not violate
and is not in conflict with any of the provisions, as applicable, of the
Certificate of Incorporation or Bylaws of Invitron Corporation, the part-
nership agreement of ACC, declaration of trust or other
<PAGE>
Tanox Biosystems, Inc.
July __,1987                                                                  5.

document or instrument by which the respective business affairs of each of the
Investors is governed and, to our knowledge, does not result in a default under
or violation of any agreement or instrument to which any of the Investors are a
party or by which they are bound, which breach or default would have a material
adverse effect on the properties, financial condition, or operations of the
Company.

     (g) The Voting Agreement has been duly executed and delivered by each of
the Investors and constitutes a valid and binding obligation of each of the
Investors. The execution, delivery and performance thereof do not and will not
violate any of the provisions, as applicable, of the Certificate of
Incorporation or Bylaws of Invitron Corporation, the partnership agreement of
ACC, declaration of trust or other document or instrument by which the
respective business affairs of each of the Investors is governed.

                                         Very truly yours,

                                         BROBECK, PHLEGER & HARRISON

                                         By
                                              Robert E. Metz
REM:tdn
<PAGE>
                                                                    EXHIBIT 10.1

                      NON-DISCLOSURE AND SECRECY AGREEMENT

     THIS AGREEMENT (hereinafter referred to as the "Agreement") is made this
the __ day of __, 1987, by and between TANOX BIOSYSTEMS, INC., a Texas
corporation (referred to as the "Company"), and __________________________
(referred to as "Prospect"), affiliates of Prospect, and officials, agents,
representatives, and employees of Prospect and such affiliates (the foregoing,
collectively with Prospect, are referred to as the "Prospect Parties").

                                R E C I T A L S:

     A. The Company has certain know-how and rights to make, use and sell a
patented process relating to the determination of antigenic substances by
antibody-coated spots on a matrix (the "Patented Process") and, in addition
thereto, has developed and in the future may acquire or develop certain other
know-how, secret methods, procedures, and technology, ("Proprietary Technology")
including, without limitation, know-how related to use of the Patented Process
and know-how and trade secrets relating to, among other things, immunity against
HTLV retro-viruses and medical diagnosis, prophylaxis and therapy against
Acquired Immune Deficiency Syndrome ("AIDS") , which Proprietary Technology will
be identified as such to the Prospect Parties at the time of any disclosure of
same. The Prospect Parties desire to review the Patented Process and Proprietary
Technology to assess the significance and value of same in connection with
considering possible investment in the Company or such technology, in whole or
in part, and, upon such investment, may continue to have certain access to such
Proprietary Technology.

     B. During the course of such discussions and thereafter if an investment is
made, the Company may disclose to the Prospect Parties or permit them to review
both the Patented Process and Proprietary Technology and certain other
information concerning the business of the Company which the Company desires to
protect and preserve in confidence, including, without limitation, names of
customers and suppliers, technical data, records, documents, specifications,
operating and marketing techniques, business procedures and methods, financial
reports and related proprietary information of the Company (all of which is
referred to as the
<PAGE>
"Confidential Information"), which Confidential Information will be identified
as such to the Prospect Parties at the time of any disclosure of same.

     C. Notwithstanding anything to the contrary contained in Recitals A or B
above, no information supplied by the Company shall be deemed or considered to
be Proprietary Technology or Confidential Information unless (i) if supplied in
written form, the same is conspicuously identified as being proprietary or
confidential, or (ii) if disclosed or supplied orally, the same is confirmed in
written summary form within thirty (30) days of the oral disclosure and
conspicuously identified as being proprietary or confidential.

     Accordingly, in consideration of the foregoing, and of the agreement of the
Company to pursue such discussions, and subject to the acknowledgment hereby of
the Prospect that such information is provided to them in reliance upon the
relationship of confidence created hereby, the parties agree as follows:

1.   OBLIGATIONS OF CONFIDENCE

     1.l The Prospect agrees, represents and covenants that the Prospect
Parties:

          (a) Will not disclose such Proprietary Technology or Confidential
Information to others;

          (b) Will not use it, directly or indirectly, for their own account or
benefit;

          (c) will not make, disclose or distribute, directly or indirectly,
documents or copies of documents containing disclosures of such Proprietary
Technology or Confidential Information, except to persons constituting the
Prospect Parties;

          (d) As to any confidential documents which may be reviewed or
delivered as a part of the meetings between the Company and the Prospect
Parties, will treat them confidentially and mark them, if necessary, prior to
distribution to other of the Prospect Parties, as proprietary, confidential
documents not to be reproduced or otherwise used without the written consent of
the Company;

                                       -2-
<PAGE>
                                 EXHIBIT 10.7.1
<PAGE>
                       [TANOX BIOSYSTEMS, INC. LETTERHEAD]

October 27, 1989
Shireen Alafi and
Christopher Alafi
c/o Moshe Alafi
P. O. Box 7338
Berkeley, California 94707

Dear Shireen and Christopher:

     As you know, we are currently seeking additional financing for the Company.
Transactions currently being discussed include additional offerings of Tanox
common stock and the equipment loan transaction now pending with Phoenix Venture
Incorporated.

     Under the terms of the Stock Purchase Agreement dated July 14, 1987, among
you, the Company and certain other shareholders, you retained certain rights
with respect to subsequent offers of common stock and certain registration
rights covering the shares which you acquired. To facilitate completion of the
additional financing ttansactions contemplated, we would like to obtain your
agreement to the following:

     1. That you do not intend to exercise your right of first refusal with
respect to future sales by the Company of its common stock and that your rights
under Section 9 are agreed to be terminated and not be applicable to any
financing transactions, including offers or sales of common stock, convertible
securities, or options to acquire such securities, following this date; and

     2. That the Company can enter into an agreement with any holder or
prospective holder of securities of the Company that will allow such holder to
include such securities in any registration of securities in which you would be
entitled to participate under the provisions of Section 7, if the inclusion of
such holder's securities would not reduce your registration rights on other than
a prorata basis (based on the number of shares owned); and that such holders
would be subject to any applicable limitations or obligations on a prorata
basis, including the requirements of Section 7.6 "Underwriting Requirements"
which permit the underwriters in any offering involving an underwriting of
shares to limit, in accordance with such section, the number of shares which may
be included by selling shareholders.
<PAGE>
     If you are willing to agree to the above please sign and date the enclosed
duplicate origina1 of this 1etter and return it to us your earliest convenience.

                                             Yours truly,

                                             /s/ NANCY T. CHANG
                                             Nancy T. Chang
                                             President

ACKNOWLEDGED AND AGREED:

/s/ SHIREEN ALAFI
Shireen Alafi

DATE: _________, 1989

/s/ CHRISTOPHER ALAFI
Christopher Alafi

DATE: _________, 1989
<PAGE>
                                 EXHIBIT 10.7.2
<PAGE>
                      [TANOX BIOSYSTEMS, INC. LETTERHEAD]

                                October 27, 1989
Alafi Capital Company
Ann: Moshe Alafi, General Partner
P.O. Box 7338
Berkeley, California 94707

Dear Moshe:

     As you know, we are currently seeking additional financing for the Company.
Transactions currently being discussed include additional offerings of Tanox
common stock and the equipment loan transaction now pending with Phoenix Venture
Incorporated.

     Under the terms of the Stock Purchase Agreement dated July 14, 1987, among
you, the Company and certain other shareholders, you retained certain rights
with respect to subsequent offers of common stock and certain registration
rights covering the shares which you acquired. To facilitate completion of the
additional financing transactions contemplated, we would like to obtain your
agreement to the following:

     1. That you do not intend to exercise your right of first refusal with
respect to future sales by the Company of its common stock and that your rights
under Section 9 are agreed to be terminated and not be applicable to any
financing transactions, including offers or sales of common stock, convertible
securities, or options to acquire such securities, following this date; and

     2. That the Company can enter into an agreement with any holder or
prospective holder of securities of the Company that will allow such holder to
include such securities in any registration of securities in which you would be
entitled to participate under the provisions of Section 7, if the inclusion of
such holder's securities would not reduce your registration rights on other than
a pro rata basis (based on the number of shares owned); and that such holders
would be subject to any applicable limitations or obligations on a pro rata
basis, including the requirements of Section 7.6 "Underwriting Requirements"
which permit the underwriters in any offering involving an underwriting of
shares to limit, in accordance with such section, the number of shares which may
be included by selling shareholders.
<PAGE>
     If you are willing to agree to the above, please sign and date the enlcosed
duplicate origina1 of this 1etter and return it to us your earliest
convenience.

                                             Yours truly,

                                             /s/ NANCY T. CHANG
                                             Nancy T. Chang
                                             President

ACKNOWLEDGED AND AGREED:

Alafi Capital Company

/s/ MOSHE ALAFI
By: Moshe Alafi, General Partner

Date: _____________, 1989.
<PAGE>
                                 EXHIBIT 10.7.3
<PAGE>
                       [INVITRON CORPORATION LETTERHEAD]

November 13, 1989

Nancy T. Chang, Ph.D.
President
Tanox Biosystems, Inc.
10301 Stella Link
Houston, TX 77025

Dear Nancy:

This letter is being sent to you at your request to permit you to complete the
equipment loan transaction now pending with Phoenix Venture Incorporated
("Phoenix Transaction").

Under the terms of the Stock Purchase Agreement dated July 14, 1987 (the "SPA"),
among Invitron, Tanox Biosystems, Inc. ("the Company") and certain other
shareholders, Invitron retained certain rights with respect to subsequent offers
of common stock and certain registration rights covering the shares which
Invitron acquired. To facilitate completion of the Phoenix Transaction, Invitron
agrees to the following:

     1. Invitron waives any rights that it may have under its right of first
refusal with respect to the Phoenix Transaction and agrees that such transaction
may be completed without violation of such rights; provided, that Invitron
reserves its right of first refusal under Section 9 of the SPA with respect to
future sales of securities by the Company, and Tanox agrees to extend such
right.

     2. Tanox can enter into an agreement with any holder or prospective holder
of securities of Tanox that will allow such holder to include such securities
in any registration of securities in which Invitron would be entitled to
participate under the provisions of Section 7, if the inclusion of such holder's
securities will not reduce Invitron's registration rights on other than a
prorata basis (based on the number of shares owned); and that such holders will
be subject to any applicable limitations or obligations on a pro rata basis,
including requirements of Section 7.6 "Underwriting Requirements" which permit
the underwriters in any offering involving an underwriting of shares to limit,
in accordance with such section, the number of shares which may be included by
selling shareholders.

Please let us know if we can be of any further assistance in connection with the
completion of the Phoenix Transaction.

Sincerely,

/s/ JOHN T. W. HAWKINS
John T. W. Hawkins
Senior Vice President, Finance
Chief Financial Officer
<PAGE>
                                 EXHIBIT 10.7.4
<PAGE>
                      [TANOX BIOSYSTEMS, INC. LETTERHEAD]

August 10, 1990                                              Via Federal Express

Dr. H. F. Mohr
Head of Pharma Licensing
CIBA-GEIGY Limited
CH4002 Basle, Switzerland

     Re: Acquisition of Tanox's Shares from Invitron

Dear Dr. Mohr:

     This letter is intended to reflect the conclusions we have reached in our
telephone conversation today as a follow-up to the correspondence from Dr. Nancy
Chang to you on August 9 and your response of today.

     With respect to Ciba Geigy's anti-dilution rights, we agreed that purchase
transactions, such as the Invitron transaction, will not influence at all the
rights and obligations under our Stock Purchase Agreement (the "Agreement"),
including those relating to anti-dilution under Section 6.04. Specifically,
Ciba-Geigy will continue to have anti-dilution rights as they currently exist
(at 7.3% ownership interest) or at the increased levels that result from
additional purchases of Tanox Common Stock under the Agreement, notwithstanding
any purchases of Tanox stock outside the Agreement. Tanox also will continue to
provide Ciba-Geigy with notice of all applicable stock transactions as required
under the Agreement so that Ciba-Geigy can exercise its anti-dilution rights, if
desired. However, Ciba-Geigy also will have the right to timely advise Tanox
that it desires to apply shares acquired from Invitron, as necessary, toward
maintaining its anti-dilution rights at the level then applicable under the
Agreement to avoid a reduction of such rights.

     Functionally, this means that after the closing of your transaction with
Invitron, Tanox will still be obligated to give Ciba-Geigy the opportunity to
purchase 7.3% of the shares being offered in the pending private placement
transaction. Ciba-Geigy then will make a decision of whether or not it desires
to acquire such shares.

     Also, as we have discussed, our consent to Ciba-Geigy's purchase of Tanox
Common Stock owned by Invitron Corporation is based on our understanding as
follows: (i) that such stock will be acquired subject to the provisions of that
certain Voting Agreement among Invitron, Tanox, and other parties thereto, dated
July 14, 1987 and (ii) that the only rights outstanding under that certain
Stock Purchase Agreement among Invitron, Tanox, and other parties thereto, dated
July 14, 1987, are the registration rights contained in Section 7, as
supplemented by paragraph 2 of the Invitron letter dated November 13, 1989,
included with
<PAGE>
Dr. H. F. Mohr
August 10, 1990
Page Two

this letter (the rights of first refusal referenced in paragraph one were
subsequently terminated as a result of Invitron's failure to exercise them in
connection with Ciba-Geigy's purchase of Tanox stock), and rights under Section
8 to receive certain financial information (which rights Ciba-Geigy already has
under our Agreement).

     If this letter correctly reflects our mutual understandings and agreements,
please execute the duplicate original of this letter to confirm same.

     To permit your transaction with Invitron to proceed without delay, we also
are sending a copy of this letter via fax and will accept evidence of execution
of this letter via fax, pending your return of one duplicate original.

     Please let me know if you have any questions or additional comments.

                                             Yours truly,

                                             /s/ DAVID ANDERSON
                                             David Anderson
                                             Executive Vice President

Acknowledged and Agreed:

CIBA-GEIGY Limited

By: /s/ H. F. MOHR
Name: H. F. Mohr
Title: Head of Pharma Licensing

By:: /s/ M. CLAUSEN
Name:  M. Clausen
Title: Head of Licensing Office

DA:nk

cc: Dr. Nancy T. Chang