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                                                                     EXHIBIT 3.3

                                     BYLAWS
                                       OF
                          OPTICAL SENSORS INCORPORATED
                             A Delaware Corporation
                               (the "Corporation")
                     (As amended through September 9, 1998)

                                   ARTICLE I.
                                   ----------

                                     OFFICES
                                     -------

        Section 1. Registered Office. The registered office of the Corporation
required by the Delaware General Corporation Law to be maintained in the State
of Delaware is as designated in the Certificate of Incorporation. The Board of
Directors of the Corporation may, from time to time, change the location of the
registered office. On or before the day that such change is to become effective,
a certificate of such change and of the new address of the new registered office
shall be filed with the Secretary of State of the State of Delaware.

        Section 2. Other Office. The Corporation may also have offices at such
other places, both within and without the State of Delaware, as the Board of
Directors may from time to time determine or the business of the Corporation may
require.

                                  ARTICLE II.
                                  -----------

                            MEETINGS OF STOCKHOLDERS
                            ------------------------

        Section 1. Place and Time of Annual Meeting. An annual meeting of the
stockholders shall be held for the purpose of electing directors and conducting
such other business as may come before the meeting. The date, time and place of
the annual meeting shall be determined by resolution of the Board of Directors.
At each annual meeting, the stockholders entitled to vote shall elect a Board of
Directors and they may transact such other business as shall be stated in the
notice of the meeting.

        Section 2. Special Meetings. Special meetings of the stockholders, for
any purpose or purposes, unless otherwise prescribed by statute or by the
Certificate of Incorporation, may be called by the Chief Executive Officer and
shall be called by the Chief Executive Officer at the request in writing of (a)
two or more members of the Board of Directors, (b) stockholders holding fifty
percent (50%) or more of the voting power of all shares entitled to vote, (c)
stockholders owning at least twenty-five percent (25%) or more of the
outstanding shares of the Corporation's Series B Convertible Preferred Stock,
but only for so long as any such shares are outstanding, or (d) stockholders
owning at least twenty-five percent (25%) or more of the outstanding shares of
the Corporation's Series C Convertible Preferred Stock, but only for so long as
any such shares are outstanding. Such requests, which shall be by registered
mail or delivered in person to the Chief Executive Officer, and shall state the
purpose or purposes of the proposed meeting.
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        Section 3. Notice. Written or printed notice of every annual or special
meeting of the stockholders, stating the place, date, time, and, in the case of
special meetings, the purpose or purposes, of such meeting, shall be given to
each stockholder entitled to vote at such meeting not less than ten, nor more
than sixty, days before the date of the meeting. All such notices shall be
delivered, either personally or by mail, and if mailed, such notice shall be
deemed to be delivered when deposited in the United States mail addressed to the
stockholder at his or her address at it appears on the records of the
Corporation, with postage prepaid.

        Section 4. Waiver of Notice. Whenever any notice is required to be given
under the provisions of the statutes, or of the Certificate of Incorporation or
of these Bylaws, a waiver thereof in writing, signed by the person or persons
entitled to said notice, whether before or after the time stated therein, shall
be deemed equivalent thereto.

        Section 5. Stockholder's List. The officer having charge of the stock
ledger of the Corporation shall make, at least ten days before every meeting of
the stockholders, a complete list of the stockholders entitled to vote at such
meeting arranged in alphabetical order, specifying the address of and the number
of shares registered in the name of each stockholder. Such list shall be open to
the examination of any stockholder, for any purpose germane to the meeting,
during ordinary business hours, for a period of at least ten days prior to the
meeting, either at a place within the city where the meeting is to be held,
which place shall be specified in the notice of the meeting or, if not so
specified, at the place where the meeting is to be held. The list shall also be
produced and kept at the time and place of the meeting during the whole time
thereof, and may be inspected by any stockholder who is present.

        Section 6. Quorum. The holders of a majority of the stock issued and
outstanding and entitled to vote thereat, present in person or represented by
proxy, shall constitute a quorum at all meetings of the stockholders except as
otherwise provided by statute or by the Certificate of Incorporation. If a
quorum is present, the holders of the shares present in person or represented by
proxy at the meeting, and entitled to vote thereat, shall have the power, by the
affirmative vote of the holders of a majority of such shares, to adjourn the
meeting to another time and/or place. Unless the adjournment is for more than
thirty days or unless a new record date is set for the adjourned meeting, no
notice of the adjourned meeting need be given to any stockholder provided that
the time and place of the adjourned meeting were announced at the meeting at
which the adjournment was taken. At the adjourned meeting the Corporation may
transact any business which might have been transacted at the original meeting.

        Section 7. Vote Required. When a quorum is present or represented at any
meeting, the vote of the holders of a majority of the stock having voting power
present in person or represented by proxy shall decide any question brought
before such meeting, unless the question is one upon which by express provisions
of an applicable statute or of the Certificate of Incorporation a different vote
is required, in which case such express provision shall govern and control the
decision of such question.

        Section 8. Voting Rights. Every stockholder shall at every meeting of
the stockholders be entitled to one vote in person or by proxy for each share of
the capital stock

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having voting power held by such stockholder, except that no proxy shall be
voted after three years from its date, unless such proxy provides for a longer
period. An appointment of a proxy for shares held jointly by two (2) or more
stockholders is valid if signed by any one (1) of them, unless the Corporation
receives from any one (1) of those stockholders written notice either denying
the authority of that person to appoint a proxy or appointing a different proxy.
To be valid, all proxies must meet the requirements of, and shall be governed
by, the Delaware General Corporation Law.

                                  ARTICLE III.
                                  ------------

                                    DIRECTORS
                                    ---------

        Section 1. Number, Election and Term of Office. The number of directors
which shall constitute the whole board shall be at least one (1) or such other
number as shall be fixed from time to time by resolution of the Board. The
directors shall be elected at the annual meeting of the stockholders, except as
provided in Section 4 of this Article III, and each director elected shall hold
office until the next annual meeting of stockholders or until a successor is
duly elected and qualified or until his or her earlier death, resignation or
removal as hereinafter provided.

        Section 2. Management By Board of Directors. The business of the
Corporation shall be managed by its Board of Directors, which may exercise all
such powers of the Corporation and do all such lawful acts and things as are not
by statute, or by Certificate of Incorporation, or by these Bylaws directed or
required to be exercised or done by the stockholders.

        Section 3. Removal. Any director or the entire Board of Directors may be
removed at any time, with or without cause, by the holders of a majority of the
shares of stock of the Corporation then entitled to vote at an election of
directors, except as otherwise provided by statute.

        Section 4. Vacancies. Vacancies and newly created directorships
resulting from any increase in the authorized number of directors may be filled
by a majority of the directors then in office though less than a quorum, and
each director so chosen shall hold office until the next annual election or
until a successor is duly elected and qualified or until his or her earlier
death, resignation or removal as hereinafter provided.

        Section 5. Annual Meetings. The annual meeting of each newly elected
Board of Directors shall be held without other notice than this Bylaw
immediately after, and at the same place as, the annual meeting of stockholders.

        Section 6. Other Meetings and Notice. Regular meetings, other than the
annual meeting, of the Board of Directors may be held without notice at such
time and at such place as shall from time to time be determined by the board.
Special meetings of the Board of Directors may be called by or at the request of
the Chief Executive Officer on at least twenty-four hours' notice to each
director, either personally, by telephone, by mail, or by telegraph; in like
manner

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and on like notice the Chief Executive Officer must call a special meeting on
the written request of a majority of directors. Whenever any notice is required
to be given under the provisions of the statutes, or of the Certificate of
Incorporation or of these Bylaws, a waiver thereof in writing, signed by the
person or persons entitled to said notice, whether before or after the time
stated therein, shall be deemed equivalent thereto.

        Section 7. Quorum. A majority of the total number of directors shall
constitute a quorum for the transaction of business. The vote of a majority of
directors present at a meeting at which a quorum is present shall be the act of
the Board of Directors. If a quorum shall not be present at any meeting of the
Board of Directors, the directors present thereat may adjourn the meeting from
time to time, without notice other than announcement at the meeting, until a
quorum shall be present.

        Section 8. Committees. The Board of Directors may, by resolution passed
by a majority of the whole board, designate one or more committees, each
committee to consist of one or more of the directors of the Corporation, which
to the extent provided in such resolution shall have and may exercise the powers
of the Board of Directors in the management and affairs of the Corporation
except as otherwise limited by statute. The Board of Directors may designate one
or more directors as alternate members of any committee. Such committee or
committees shall have such name or names as may be determined from time to time
by resolution adopted by the Board of Directors. Each committee shall keep
regular minutes of its meetings and report the same to the Board of Directors
when required.

        Section 9. Committee Rules. Each committee of the Board of Directors may
fix its own rules of procedure and shall hold its meetings as provided by such
rules, except as may otherwise be provided by the resolution of the Board of
Directors designating such committee, but in all cases the presence of at least
a majority of the members of such committee shall be necessary to constitute a
quorum. In the event that a member and that member's alternate, if alternates
are designated by the Board of Directors as provided in Section 8 of this
Article III, of such committee is/are absent or disqualified, the member or
members thereof present at any meeting and not disqualified from voting, whether
or not such member or members constitute a quorum, may unanimously appoint
another member of the Board of Directors to act at the meeting in place of any
such absent or disqualified members.

        Section 10. Informal Action. Any action permitted to be taken at any
meeting of the Board of Directors, or of any committee thereof, may be taken
without a meeting if all members of the board or committee, as the case may be,
consent thereto in writing, and the writing or writings are filed with the
minutes of proceedings of the board or committee.

        Section 11. Participation by Conference Telephone. Directors of the
Corporation may participate in a meeting of the Board of Directors or any
committee thereof by means of conference telephone or similar communications
equipment by means of which all persons participating in the meeting can hear
each other, and participation in such a manner shall constitute presence in
person at such meeting.

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        Section 12. Compensation. The directors may be paid for expenses of
attendance at each meeting of the Board of Directors and may be paid a fixed sum
for attendance at each meeting of the Board of Directors or a stated salary. No
such payment shall preclude any director from serving the Corporation in any
other capacity and receiving compensation therefor. Members of committees
designated by the Board of Directors may be allowed like compensation for
attending committee meetings.

                                  ARTICLE IV.
                                  -----------

                                    OFFICERS
                                    --------

        Section 1. Number. The officers of the Corporation shall be chosen by
the Board of Directors and shall include a Chief Executive Officer or a
President, a Secretary and a Chief Financial Officer. The Board of Directors may
also choose a Chairman of the Board of Directors (who must be a director) and
one or more Vice Presidents, and one or more Assistant Secretaries and Assistant
Financial Officers. Any number of offices or functions of those offices may be
held or exercised by the same person unless the Certificate of Incorporation or
the Bylaws otherwise provide.

        Section 2. Election and Term of Office. The officers of the Corporation
shall be elected annually by the Board of Directors at the first meeting of the
Board of Directors held after each annual meeting of stockholders. If the
election of officers shall not be held at such meeting, such election shall be
held as soon thereafter as may be convenient. Vacancies may be filled or new
offices created and filled at any meeting of the Board of Directors. Each
officer shall hold office until the next annual meeting of the Board of
Directors or until a successor is duly elected and qualified or until his or her
earlier death, resignation or removal as hereinafter provided.

        Section 3. Removal. Any officer or agent elected or appointed by the
Board of Directors may be removed by the Board of Directors whenever in its
judgment the best interests of the Corporation would be served thereby, but such
removal shall be without prejudice of the contract rights, if any, of the person
so removed.

        Section 4. Vacancies. A vacancy in any office because of death,
resignation, removal, disqualification or otherwise, may be filled by the Board
of Directors for the unexpired portion of the term by a majority vote of the
directors then in office.

        Section 5. Compensation. Compensation of all officers shall be fixed by
the Board of Directors, and no officer shall be prevented from receiving such
compensation by virtue of the fact that he is also a director of the
Corporation.

        Section 6. Chairman of the Board of Directors. The Chairman of the Board
of Directors, if there be one, shall preside at all meetings of the stockholders
and of the Board of Directors. If there be no Chief Executive Officer or
President, the Chairman of the Board shall be the Chief Executive Officer of the
Corporation, and except where by law the signature of the Chief Executive
Officer is required, the Chairman of the Board of Directors shall possess the

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same power as the Chief Executive Officer to sign all contracts, certificates
and other instruments of the Corporation which may be authorized by the Board of
Directors. The Chairman of the Board of Directors shall also perform such other
duties and may exercise such other powers as from time to time may be assigned
to him by these By-Laws or by the Board of Directors.

        Section 7. The Chief Executive Officer. The Chief Executive Officer, if
there be one, shall be subject to the control of the Board of Directors and, if
there be one, the Chairman of the Board of Directors, have general supervision
of the business of the Corporation and shall see that all orders and resolutions
of the Board of Directors are carried into effect. He or she shall execute
bonds, mortgages and other contracts of the Corporation, except where required
or permitted by law to be otherwise signed and executed or except where the
signing and execution thereof shall be expressly delegated by the Board of
Directors to some other officer or agent of the Corporation. In the absence or
disability of the Chairman of the Board of Directors, or if there be none, the
Chief Executive Officer shall preside at all meetings of the stockholders and
the Board of Directors.

        Section 8. The President. The President, if there be one, shall be
subject to the control of the Board of Directors and, if there be one, the Chief
Executive Officer, have general supervision of the business of the Corporation
and shall see that all orders and resolutions of the Board of Directors are
carried into effect. He or she shall execute bonds, mortgages and other
contracts of the Corporation, except where required or permitted by law to be
otherwise signed and executed or except where the signing and execution thereof
shall be expressly delegated by the Board of Directors to some other officer or
agent of the Corporation. In the absence or disability of the Chairman of the
Board of Directors and the Chief Executive Officer, or if there be none, the
President shall preside at all meetings of the stockholders and the Board of
Directors. If there be no Chief Executive Officer, the President shall be the
Chief Executive Officer of the Corporation.

        Section 9. The Vice President. The vice president, if any, or if there
shall be more than one, the vice presidents in the order determined by the Board
of Directors, shall in the absence or disability of the Chief Executive Officer
(and if there be no Chairman of the Board of Directors) perform the duties and
exercise the powers of the chief executive officer and shall perform such other
duties and have such other powers as the Board of Directors may from time to
time prescribe.

        Section 10. The Secretary and Assistant Secretaries. The secretary shall
attend all meetings of the Board of Directors and all meetings of the
stockholders and record all the proceedings of the meetings of the Corporation
and of the Board of Directors in a book to be kept for that purpose and shall
perform like duties for the standing committees when required. The secretary
shall give, or cause to be given, notice of all meetings of the stockholders and
special meetings of the Board of Directors; perform such other duties as may be
prescribed by the Board of Directors or Chief Executive Officer, under whose
supervision he or she shall be. The assistant secretary, if any, or if there be
more than one, the assistant secretaries in the order determined by the Board of
Directors, shall in the absence or disability of the secretary perform

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the duties and exercise the powers of the secretary and shall perform such other
duties and have such other powers as the Board of Directors may from time to
time prescribe.

        Section 11. The Chief Financial Officer and Assistant Financial Officer.
The chief financial officer shall have the custody of the corporate funds and
securities; shall keep full and accurate accounts of receipts and disbursements
in books belonging to the Corporation; shall deposit all monies and other
valuable effects in the name and to the credit of the Corporation in such
depositories as may be designated by the Board of Directors; shall disburse the
funds of the Corporation as may be ordered by the Board of Directors, taking
proper vouchers for such disbursements; and shall render to the chief executive
officer and the Board of Directors at its regular meetings, or when the Board of
Directors so requires, an account of the Corporation. If required by the Board
of Directors, the chief financial officer shall give the Corporation a bond
(which shall be renewed every six years) in such sums and with such surety or
sureties as shall be satisfactory to the Board of Directors for the faithful
performance of the duties of the office of chief financial officer and for the
restoration to the Corporation, in case of death, resignation, retirement or
removal from office, of all books, papers, vouchers, money, and other property
of whatever kind in the possession or under the control of the chief financial
officer belonging to the Corporation. The assistant financial officer, if any,
or if there shall be more than one, the assistant financial officers in the
order determined by the Board of Directors, shall in the absence or disability
of the chief financial officer perform the duties and exercise the powers of the
chief financial officer and shall perform such other duties and have such other
powers as the Board of Directors may from time to time prescribe.

        Section 12. Other Officers, Assistant Officers and Agents. Officers,
assistant officers and agents, if any, other than those whose duties are
provided for in these Bylaws, shall have such authority and perform such duties
as may from time to time be prescribed by resolution of the Board of Directors.

                                   ARTICLE V.
                                   ----------

                              CERTIFICATE OF STOCK
                              --------------------

Section 1. Form. Every holder of stock in the Corporation shall be entitled to
have a certificate, signed by, or in the name of the Corporation by (i) the
Chairman of the Board of Directors, the Chief Executive Officer or a Vice
President and (ii) by the Chief Financial Officer or an Assistant Financial
Officer, or the Secretary or an Assistant Secretary of the Corporation,
certifying the number of shares owned by him or her in the Corporation. Where a
certificate is signed (1) by a transfer agent or an assistant transfer agent,
other than the Corporation or its employee or (2) by a registrar, other than the
Corporation or its employee, any other signature on the certificate may be
facsimile. In case any officer or officers who have signed, or whose facsimile
signature or signatures have been used on, any such certificate or certificates
shall cease to be such officer or officers of the Corporation whether because of
death, resignation or otherwise before such certificate or certificates have
been delivered by the Corporation, such certificate or certificates may
nevertheless be issued and delivered as though the person or

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persons who signed such certificate or certificates or whose facsimile signature
or signatures have been used thereon had not ceased to be such officer or
officers of the Corporation.

        Section 2. Lost Certificates. The Board of Directors may direct a new
certificate or certificates to be issued in place of any certificate or
certificates theretofore issued by the Corporation alleged to have been lost,
stolen or destroyed, upon the making of an affidavit of that fact by the person
claiming the certificate of stock to be lost, stolen or destroyed. When
authorizing such issue of a new certificate or certificates, the Board of
Directors may, in its discretion and as a condition precedent to the issuance
thereof, require the owner of such lost, stolen or destroyed certificate or
certificates, or his or her legal representative, to give the Corporation a bond
in such sum as it may direct as indemnity against any claim that may be made
against the Corporation with respect to the certificate alleged to have been
lost, stolen or destroyed.

        Section 3. Fixing a Record Date. The Board of Directors may fix in
advance not more than sixty nor less than ten days preceding the date of any
meeting of stockholders, or the date for the payment of any dividend, or the
date for the allotment of rights, or the date when any change or conversion or
exchange of capital stock shall go into effect, or a date in connection with
obtaining such consent, as a record date for the determination of the
stockholders entitled to notice of, and to vote at, any such meeting, and any
adjournment thereof, or entitled to receive payment of any such dividend, or
entitled to any such allotment of rights, or entitled to exercise the rights in
respect to any such change, conversion, or exchange of capital stock, or
entitled to give such consent, and in such case such stockholders and only such
stockholders as shall be stockholders of record on the date so fixed shall be
entitled to such notice of, and to vote at, such meeting and any adjournment
thereof, or to receive payments of such dividend, or to receive such allotment
or rights, or to exercise such rights, or to give such consents, as the case may
be, notwithstanding any transfer of any stock on the books of the Corporation
after any such record date fixed as aforesaid. If no record date is fixed, the
time for determining stockholders shall be at the close of business on the day
next preceding the day on which notice is given, or if notice is waived, at the
close of business on the day next preceding the day on which the meeting is
held. The time for determining stockholders for any other purpose shall be at
the close of business on the date on which the Board of Directors adopts the
resolution relating thereto. A determination of stockholders shall apply to any
adjournment of the meeting; provided, however, that the Board of Directors may
fix a new record date for the adjourned meeting.

        Section 4. Registered Stockholders. The Corporation shall be entitled to
recognize the exclusive right of a person registered on its books as the owner
of shares to receive dividends, and to vote as such owner, and to hold liable
for calls and assessments a person registered on its books as the owner of
shares, and shall not be bound to recognize any equitable or other claim to or
interest in such share or shares on the part of the other person, whether or not
it shall have express or other notice thereof, except as otherwise provided by
the laws of Delaware.

        Section 5. Stock Certificates and Legend. If the Corporation shall be
authorized to issue more than one class of stock or more than one series of any
class, the powers, designations, preferences and relative, participating,
optional or other special rights of each class of stock or

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series thereof and the qualifications, limitations or restrictions of such
preferences and/or rights shall be set forth in full or summarized on the face
or back of the certificate which the Corporation shall issue to represent such
class or series of stock, provided that, except as otherwise provided in Section
202 of the General Corporation Law of Delaware, in lieu of the foregoing
requirements, there may be set forth on the face or back of the certificate
which the Corporation shall issue to represent such class or series of stock, a
statement that the Corporation will furnish without charge to each stockholder
who so requests the powers, designations, preferences and relative,
participating, optional or other special rights of each class of stock or series
thereof and the qualifications, limitations or restrictions of such preferences
and/or rights.

                                  ARTICLE VI.
                                  -----------

                               GENERAL PROVISIONS
                               ------------------

        Section 1. Dividends. Dividends upon the capital stock of the
Corporation, subject to the provisions of the Certificate of Incorporation, if
any, may be declared by the Board of Directors at any regular or special
meeting, pursuant to law. Dividends may be paid in cash, in property, or in
shares of the capital stock, subject to the provisions of the Certificate of
Incorporation. Before payment of any dividend, there may be set aside out of any
funds of the Corporation available for dividends such sum or sums as the
directors from time to time, in their absolute discretion, think proper as a
reserve or reserves to meet contingencies or for equalizing dividends, or for
repairing or maintaining any property of the Corporation, or for such other
purpose as the directors shall think in the best interest of the Corporation,
and the directors may modify or abolish any such reserve in the manner in which
it was created.

        Section 2. Checks. All checks or demands for money and notes of the
Corporation shall be signed by such officer or officers or such other person or
persons as the Board of Directors may from time to time designate.

        Section 3. Fiscal Year. The fiscal year of the Corporation shall be
fixed by resolution of the Board of Directors.

        Section 4. Seal. The Corporation shall not have a corporate seal.

        Section 5. Securities Owned by Corporation. Voting securities in any
other corporation held by the Corporation shall be voted by the Chief Executive
Officer, unless the Board of Directors specifically confers authority to vote
with respect thereto, which may be general or confined to specific instances,
upon some other person or officer. Any person authorized to vote securities
shall have the power to appoint proxies, with general power of substitution.

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                                  ARTICLE VII.
                                  ------------

                                   AMENDMENTS
                                   ----------

        These Bylaws may be adopted, amended, altered or repealed at any meeting
of the Board of Directors by majority vote. The fact that the power to adopt,
amend, alter or repeal the Bylaws has been conferred upon the Board of Directors
shall not divest the stockholders of the same powers.

Dated: September 9, 1998

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