<PAGE>

                                                                       EXHIBIT 4

THE SECURITIES REPRESENTED HEREBY ARE RESTRICTED SECURITIES WITHIN THE 
MEANING OF THE SECURITIES ACT OF 1933, AS AMENDED,  AND MAY NOT BE SOLD, 
PLEDGED, TRANSFERRED OR OTHERWISE DISPOSED OF EXCEPT IN ACCORDANCE WITH SUCH 
ACT AND THE RULES AND REGULATIONS THEREUNDER AND IN ACCORDANCE WITH 
APPLICABLE STATE SECURITIES LAWS. THE ISSUER OF THESE SECURITIES WILL NOT 
TRANSFER SUCH SECURITIES EXCEPT UPON RECEIPT OF EVIDENCE SATISFACTORY TO THE 
ISSUER THAT THE REGISTRATION PROVISIONS OF SUCH ACT HAVE BEEN COMPLIED WITH 
OR THAT SUCH REGISTRATION IS NOT REQUIRED AND THAT SUCH TRANSFER WILL NOT 
VIOLATE ANY APPLICABLE STATE SECURITIES LAWS.

                7.5% CONVERTIBLE DEBENTURE DUE FEBRUARY 28, 1999

$100,000                                                          March 11, 1997

     FOR VALUE RECEIVED, SALIVA DIAGNOSTIC SYSTEMS, INC., a Delaware 
corporation (the "Company"), hereby promises to pay to the order of The Tail 
Wind Fund Ltd., or its registered assigns (the "Holder") on February 28, 1999 
(the "Maturity Date"), the principal amount of One Hundred Thousand Dollars 
($100,000) and to pay interest on the principal amount hereof, in such 
amounts, at such times and on such terms and conditions as are specified 
herein.  This Debenture (the "Debenture") has been issued pursuant to that 
certain Convertible Securities Subscription Agreement executed between the 
Holder and the Company, dated March 11, 1997 (the "Agreement").

ARTICLE 1.     INTEREST.

     The Company shall pay interest on the unpaid principal amount of this 
Debenture at the rate equal to Seven and One-half Percent (7.5%) per year, 
compounded annually, payable upon conversion or redemption of the Debenture 
as set forth below, until the principal hereof is paid in full or has been 
converted.  Interest shall be payable, at the option of the Company, in cash 
or by issuing such number of additional shares of common stock of the 
Company, par value $.01 per share (the "Common Stock"), as is determined by 
dividing the total dollar amount of interest due and payable by the Current 
Market Price (as defined in SECTION 3.7 below) of the Common Stock on the 
date of such interest payment.  All Common Stock issued as interest in 
respect of the Debenture will be, when so issued, duly authorized, validly 
issued, fully paid and non-assessable and free of all liens and charges.  
Interest on this Debenture shall accrue from the most recent date to which 
interest has been paid or, if no interest has been paid, from March 11, 1997. 
 Interest shall be computed on the basis of a 360-day year of twelve 30-day 
months.

ARTICLE 2.     METHOD OF PAYMENT.

     This Debenture must be surrendered to the Company in order for the 
Holder to receive payment of the principal amount hereof.  The Company shall 
pay the principal of and interest on this Debenture in United States dollars. 
 Interest and principal payments shall be subject to withholding (if any) 
under applicable United States Federal Internal Revenue Service Regulations.

<PAGE>

ARTICLE 3.     CONVERSION.

     SECTION 3.1.   CONVERSION PRIVILEGE

     (a)  The Holder of this Debenture shall have the right, exercisable at 
one or more times, at its option, to convert up to (i) Thirty-Three and 
One-Third percent (33 1/3%) of the Debentures originally issued to the Holder 
at any time from and after the ninetieth (90th) day following the date of the 
Debentures,  (ii) up to an aggregate of Sixty-Six and Two-Thirds percent (66 
2/3%) of the Debentures originally issued to the Holder at any time from and 
after the one hundred twentieth (120th) day following the date of the 
Debentures, and (iii) One Hundred percent (100%) of the Debentures originally 
issued to the Holder at any time from and after the one hundred fiftieth 
(150th) day following the date of the Debentures. The number of shares of 
Common Stock issuable upon the conversion of this Debenture is determined by 
dividing the principal amount hereof to be converted by the Conversion Price 
(as defined in paragraph (b) of this SECTION 3.1 below) in effect on the 
Conversion Date (as defined below) and rounding the result to the nearest 
1/100th of a share.  Upon conversion, all accrued and unpaid interest on the 
amount so converted will be paid to the Holder in cash or Common Stock, as 
specified in ARTICLE 1 above.  Less than all of the principal amount of this 
Debenture may be converted into Common Stock if the portion converted is 
$1,000 or a whole multiple of $1,000, and the provisions of this ARTICLE 3 
that apply to the conversion of this Debenture also apply to the conversion 
of a portion of it.  

     (b)  Subject to ARTICLE 5 below, the Conversion Price (defined below) 
shall be the LESSER of (i) the Current Market Price as of the date of 
issuance of the Debenture MULTIPLIED BY 115% (the "Fixed Conversion Price"), 
or (ii) the product of the Current Market Price with respect to the 
applicable conversion date MULTIPLIED BY 80% (the "Floating Conversion 
Price"). The applicable price shall be referred to herein as the "Conversion 
Price."

     (c)  Notwithstanding anything contained herein to the contrary, if the 
Company would be obligated to issue, upon conversion of this Debenture, more 
than that aggregate number of shares of Common Stock equal to 20% of the 
Company's outstanding Common Stock as of March 11, 1997 (the "Maximum Number 
of Shares of Common Stock"), then the Company may in its sole discretion 
redeem out of funds legally available therefor such amount of this Debenture, 
for the price set forth in Article 4(a) until the number of shares of Common 
Stock previously issued and outstanding and issuable upon conversion of this 
Debenture is equal to the Maximum Number of Shares of Common Stock (the 
"Dilution Redemption"). The Company shall pay in full the applicable 
redemption amount by wire transfer within five business days of the Company's 
notice of its election to effect a redemption under this SECTION 3.1(c).  
Until such payment, the Company shall comply with all terms, conditions and 
covenants of this Debenture.  Nothing herein shall affect the Company's 
obligation to convert this Debenture upon presentation for conversion by the 
Holder, except that the Company may, following its notice of its election to 
redeem, convert only such portion of the Debentures as it shall have elected 
not to redeem.

     (d)  Subject to the provisions of SECTION 3.1(c), in the event any, or any
portion of this, Debenture remains outstanding on the second anniversary of the
date hereof, the unconverted portion of this Debenture will automatically be
converted into Common Stock on such date in the manner set forth in this SECTION
3.1; provided (i) an Event of Default does not then exist under this Debenture
and (ii) a registration statement as contemplated by ARTICLE 4 of the Agreement
is effective with respect to the sale by the Holder of Common Stock issuable
upon conversion of this Debenture.

     SECTION 3.2.   CONVERSION PROCEDURE.  To convert this Debenture into Common
Stock the Holder must (a) complete and sign the Notice of Conversion attached
hereto and (b) surrender the Debenture to 


                                     -2-

<PAGE>

the Company.  Except as otherwise provided herein, the date upon which the 
Company receives the completed Notice of Conversion (by recognized overnight 
courier, hand-delivery, facsimile or otherwise) is the Conversion Date, 
provided that the Company shall not be required to deliver a certificate for 
shares of Common Stock unless and until the Company receives the original 
Debenture.  Within three (3) business days after receipt of the Notice of 
Conversion as aforesaid, provided the Company has received the original 
Debenture from the Holder, the Company shall deliver a certificate with a 
restrictive legend as specified in the Agreement for the number of full 
shares of Common Stock issuable upon the conversion and a check for any 
fraction of a share.  The person in whose name the certificate representing 
shares of Common Stock is to be registered shall be treated as a stockholder 
of record on and after the Conversion Date.  Upon conversion, unpaid interest 
on the Debenture shall be paid in cash or Common Stock by the Company as set 
forth in Section 1 above.  If one person converts more than one Debenture at 
the same time, the number of full shares issuable upon the conversion shall 
be based on the total principal amount of Debentures converted.  Upon 
surrender of a Debenture that is to be converted in part, the Company shall 
issue to the Holder a new Debenture equal in principal amount to the 
unconverted portion of the Debenture surrendered.  Notwithstanding the 
foregoing, the conversion right of the Holder set forth herein shall be 
limited, solely to the extent required, from time to time, such that in no 
instance shall the maximum number of shares of Common Stock into which the 
Holder may convert this Debenture, at any one time, exceed an amount equal to 
(i) 4.9999% of the then issued and outstanding shares of Common Stock of the 
Company following such conversion (such percentage to be calculated in 
accordance with Rule 13d-3, promulgated under the Securities Exchange Act of 
1934), minus (ii) the number of shares of Common Stock of the Company then 
held by the Holder.

     SECTION 3.3.   FRACTIONAL SHARES.  The Company shall not issue any
fractional shares of Common Stock upon the conversion of this Debenture. 
Instead, the Company shall pay in lieu of any fractional shares the cash value
thereof at the then Current Market Price of the Common Stock as determined under
SECTION 3.7 below.

     SECTION 3.4.   TAXES ON CONVERSION.  The Company shall pay any documentary,
stamp or similar issue or transfer tax due on the issue of Common Stock upon the
conversion of this Debenture.  However, the Holder shall pay any such tax which
is due because such shares are issued in a name other than its name.

     SECTION 3.5.   COMPANY TO RESERVE STOCK.  The Company shall reserve out of
its authorized but unissued Common Stock enough shares of Common Stock to permit
the conversion in full of this Debenture.  All shares of Common Stock issuable
upon the conversion hereof shall be, when issued in accordance herewith, duly
authorized, validly issued, fully-paid and nonassessable.

     SECTION 3.6.   RESTRICTIONS ON TRANSFER.  This Debenture and the Common
Stock issuable upon the conversion hereof have not been registered under the
Securities Act of 1933, as amended (the "Securities Act"), and have been sold
pursuant to an exemption under the Securities Act.  The Debenture and such
Common Stock may not be transferred or resold except pursuant to registration
under or an exemption from the Securities Act.

     SECTION 3.7.   CURRENT MARKET PRICE.

          (a)  As used herein, the "Current Market Price" per share of Common
Stock on any date is the average of the quoted bid prices of the Common Stock
for the five (5) consecutive trading days ending on the trading day immediately
prior to the date in question.


                                     -3-

<PAGE>

          (b)  As used in this SECTION 3.7, the term "quoted bid price" shall
mean the closing bid price thereof on any such trading date, as reported by the
Nasdaq Stock Market.

ARTICLE 4.     REDEMPTION

     (a)  If the Current Market Price is less than $0.70 per share (subject to
recapitalizations, reclassifications and other similar events), then the Company
may, at its option, by delivering notice as set forth below, redeem all or part
this Debenture for an amount equal to the product of (x) the principal amount so
to be redeemed multiplied by (y) 125%, plus all accrued and unpaid interest
thereon.

     (b)  Any notice of exercise of the Company's redemption option pursuant to
ARTICLE 4 shall be delivered in writing to Holder and shall be irrevocable when
delivered (an "Article 4 Notice").  The Company shall pay in full the applicable
redemption amount by wire transfer within five business days of the delivery of
an Article 4 Notice.  Until such payment, the Company shall comply with all
terms, conditions and covenants of the Debenture, including without limitation,
timely payment of accrued and unpaid interest. If the Company fails to pay in
full such applicable redemption amount within such five business day period, the
Company's Article 4 Notice with respect to such redemption shall be deemed void
and the Company shall no longer be entitled to redeem the Debentures prior to
their maturity.  Subject to the foregoing, Holder's right to convert this
Debenture (or such portion hereof as the Company shall have elected to redeem)
shall be suspended but solely with respect to the portion of the Debentures to
be redeemed after delivery of the Article 4 Notice.

ARTICLE 5.     RECAPITALIZATIONS, MERGERS, ETC.

     SECTION 5.1.   RECAPITALIZATIONS GENERALLY.  In case the Company shall
(i) subdivide its outstanding Common Stock (including by means of a dividend or
distribution on the Common Stock payable in Common Stock), (ii) combine its
outstanding Common Stock into a smaller number of shares, or (iii) issue by
capital reorganization or reclassification of its Common Stock or otherwise
(other than a subdivision or combination of its shares provided for above, or a
reorganization, merger, consolidation or sale of assets provided for elsewhere
in this ARTICLE 5) any shares of capital stock of the Company, the Fixed
Conversion Price and the Maximum Number of Shares of Common Stock in effect
immediately prior to such action, shall be adjusted so that the Holder of this
Debenture thereafter surrendered for conversion shall be entitled to receive the
number of shares of capital stock of the Company which such holder would have
owned immediately following such action had this Debenture been converted
immediately prior thereto.  An adjustment made pursuant to this subsection shall
become effective retroactively immediately after the effective date in the case
of a subdivision, combination or reclassification.

     SECTION 5.2.   CERTAIN OTHER RECAPITALIZATIONS.  In case the Company shall,
during the five consecutive trading day period applicable (pursuant to SECTION
3.7(a)) in determining the Current Market Price per share of Common Stock with
respect to any conversion date, (i) subdivide its outstanding Common Stock
(including by means of a dividend or distribution on the Common Stock payable in
Common Stock), (ii) combine its outstanding Common Stock into a smaller number
of shares or, (iii) issue by capital reorganization or reclassification of its
Common Stock or otherwise (other than a subdivision or combination of its shares
provided for above, or a reorganization, merger, consolidation or sale of assets
provided for elsewhere in this ARTICLE 5) any shares of capital stock of the
Company, then, for purposes of calculating the Floating Conversion Price
applicable to such conversion, the closing bid price for the Company's Common
Stock as reported by the Nasdaq Stock Market for any day prior to such action
which falls within such five trading day period applicable to such conversion
shall be adjusted to a price per share giving effect to such action.


                                     -4-

<PAGE>

     SECTION 5.3.   MERGERS.  Until the Debentures are paid in full or have 
been converted into Common Stock, the Company shall not consolidate or merge 
into, or transfer all or substantially all of its assets to, any person, 
unless such person assumes all of the obligations of the Company under this 
Debenture and immediately after such transaction no Event of Default exists.  
Any reference herein to the Company shall refer to such surviving or 
transferee corporation and the obligations of the Company shall terminate 
upon such assumption.  If the Company merges or consolidates with another 
corporation or sells or transfers all or substantially all of its assets to 
another person and the holders of the Common Stock are entitled to receive 
stock, securities or property in respect of or in exchange for Common Stock, 
then as a condition of such merger, consolidation, sale or transfer, either 
(i) the Company and any such successor, purchaser or transferee shall amend 
this Debenture to provide that it may thereafter be converted on the terms 
and subject to the conditions set forth above into the kind and amount of 
stock, securities or property receivable upon such merger, consolidation, 
sale or transfer by a holder of the number of shares of Common Stock into 
which this Debenture might have been converted immediately before such 
merger, consolidation, sale or transfer, or (ii) if the Company is not the 
surviving entity in such merger, consolidation, sale or transfer, the Company 
shall give the Holder at least 30 days prior written notice of the expected 
closing date of such transaction, and if any portion of this Debenture has 
not been converted into Common Stock at the election of the Holder prior to 
such closing, then the remaining principal amount of this Debenture may, at 
the option of the successor, purchaser or transferee, be converted into 
shares of Common Stock at the closing of such transaction.  In any such case, 
appropriate adjustment shall be made in the application of the provisions of 
this ARTICLE 5 with respect to the rights of the Holder after such merger, 
consolidation, sale or transfer to the end that the provisions of this 
ARTICLE 5 (including adjustment of the Conversion Price then in effect and 
the number of shares issuable upon conversion of this Debenture) shall be 
applicable after that event as nearly equivalently as may be practicable.  
Except as otherwise provided herein, the Conversion Price shall be the same 
as the applicable Conversion Price defined in ARTICLE 3 above.

 ARTICLE 6.    REPORTS.

     The Company shall mail to the Holder hereof at its address as shown on 
the Register (as defined in SECTION 8.2) a copy of any annual, quarterly or 
current report that it files with the Securities and Exchange Commission 
promptly after the filing thereof and a copy of any annual, quarterly or 
other report or proxy statement that it gives to its stockholders generally 
at the time such report or statement is sent to stockholders.

ARTICLE 7.     DEFAULTS AND REMEDIES.

     SECTION 7.1.  EVENTS OF DEFAULT.  An "Event of Default" occurs if any of 
the following occur: (a) the Company does not make the payment of the 
principal of this Debenture when the same becomes due and payable at 
maturity, upon redemption or otherwise, (b) the Company does not make a 
payment of interest when such interest becomes due and payable and such 
default continues for a period of seven (7) days thereafter, (c) the Company 
fails to issue Common Stock upon conversion, within the time period specified 
in SECTION 3.2, (d) the Company fails to comply with any of its other 
agreements in this Debenture and such failure continues for the period and 
after the notice specified below, (e) the Company's Common Stock ceases to be 
quoted on any of the New York Stock Exchange, American Stock Exchange, the 
Nasdaq National Market or Nasdaq SmallCap Market for a period in excess of 10 
calendar days, (f) any of the representations or warranties made by the 
Company herein, in the Agreement, or in any historical financial statements 
heretofore furnished by the Company in connection with the execution and 
delivery of this Debenture or the Agreement shall be false or misleading in 
any material respect as of the date made (it being understood that this 
SECTION 7.1(f) shall not apply to any financial projections or other forward -


                                     -5-

<PAGE>

looking information), (g) the Company shall default on the payment of any 
debts in excess of $100,000 beyond any applicable grace period, (h) any 
judgments, levies or attachments shall be rendered against the Company or any 
of its assets or properties in an aggregate amount in excess of $100,000 and 
such judgments, levies or attachments shall not be dismissed, stayed, bonded 
or discharged within thirty (30) days of the date of entry thereof, or (i) 
the Company pursuant to or within the meaning of any Bankruptcy Law (as 
hereinafter defined): (i) commences a voluntary case; (ii) consents to the 
entry of an order for relief against it in an involuntary case; (iii) 
consents to the appointment of a Custodian (as hereinafter defined) of it or 
for all or substantially all of its property; (iv) makes a general assignment 
for the benefit of its creditors; or (v) a court of competent jurisdiction 
enters an order or decree under any Bankruptcy Law that: (A) is for relief 
against the Company in an involuntary case; (B) appoints a Custodian of the 
Company or for all or substantially all of its property; or (C) orders the 
liquidation of the Company, and the order or decree remains unstayed and in 
effect for 60 days.  As used in this SECTION 7.1, the term "Bankruptcy Law" 
means Title 11 of the United States Code or any similar Federal or State law 
for the relief of debtors or such other applicable laws and the term 
"Custodian" means any receiver, trustee, assignee, liquidator or similar 
official under any Bankruptcy Law.

     SECTION 7.2.   ACCELERATION.  If an Event of Default occurs and is 
continuing, the Holder hereof by notice to the Company may declare the 
principal of and accrued interest on this Debenture to be due and payable.  
Upon such declaration, the principal and interest hereof shall be due and 
payable immediately without presentment, demand, protest or notice of any 
kind, all of which are hereby expressly waived, anything herein or in any 
note or other instruments contained to the contrary notwithstanding, and the 
Holder may immediately, and without expiration of any period of grace, 
enforce any and all of the Holder's rights or remedies afforded by law.  The 
Company expressly waives demand and presentment for payment, notice of 
nonpayment, protest, notice of protest, notice of dishonor, notice of 
acceleration or intent to accelerate, bringing of suit and diligence in 
taking any action to collect amounts called for hereunder and the Company 
shall be directly and primarily liable for the payment of all sums owing and 
to be owing hereon, regardless of and without any notice, diligence, act or 
omission as or with respect to the collection of any amount called for 
hereunder.

ARTICLE 8.     REGISTERED DEBENTURES.

     SECTION 8.1.   SERIES.  This Debenture is one of a numbered series of 
Debentures issued to the Holder and designated as "7.5% Convertible 
Debentures Due February 28, 1999."  Such Debentures are referred to herein 
collectively as the "Debentures."

     SECTION 8.2.   RECORD OWNERSHIP.  The Company shall maintain a register 
of the holders of the Debentures (the "Register") showing their names and 
addresses and the serial numbers and principal amounts of Debentures issued 
to or transferred of record by them from time to time.  The Register may be 
maintained in electronic, magnetic or other computerized form.  The Company 
may treat the person named as the Holder of this Debenture in the Register as 
the sole owner of the Debenture.  The Holder of the Debenture is the person 
exclusively entitled to receive payments of interest and principal on the 
Debenture, receive notifications with respect to the Debenture, convert it 
into Common Stock and otherwise exercise all of the rights and powers as the 
absolute owner hereof.

     SECTION 8.3.   REGISTRATION OF TRANSFER.  Transfers of this Debenture 
may be registered on the books of the Company maintained for such purpose 
pursuant to SECTION 8.2 above (i.e., the Register).  Transfers shall be 
registered when this Debenture is presented to the Company with a request to 
register the transfer hereof and the Debenture is duly endorsed by the 
appropriate person, reasonable assurances are given that the endorsements are 
genuine and effective, and the Company has received evidence 


                                     -6-

<PAGE>

satisfactory to it that such transfer is rightful and in compliance with all 
applicable laws, including tax laws and State and Federal securities laws.  
When this Debenture is presented for transfer and duly transferred hereunder, 
it shall be canceled and a new Debenture showing the name of the transferee 
as the record holder thereof shall be issued in lieu hereof.  When this 
Debenture is presented to the Company to exchange it for an equal aggregate 
principal amount of Debentures of other denominations, the Company shall make 
such exchange and shall cancel this Debenture and issue in lieu thereof 
Debentures having a total principal amount equal to this Debenture in the 
denominations requested by the Holder.

     SECTION 8.4.   WORN AND LOST DEBENTURES.  If this Debenture becomes 
worn, defaced or mutilated but is still substantially intact and 
recognizable, the Company or its agent may issue a new Debenture in lieu 
hereof upon its surrender.  Where the Holder of this Debenture claims that 
the Debenture has been lost, destroyed or wrongfully taken, the Company shall 
issue a new Debenture in place of the original Debenture if the Holder so 
requests by written notice to the Company actually received by the Company 
before it is notified that the Debenture has been acquired by a bona fide 
purchaser and the Holder has delivered to the Company an indemnity bond in 
such amount and issued by such surety as the Company deems satisfactory 
together with an affidavit of the Holder setting forth the facts concerning 
such loss, destruction or wrongful taking and such other information in such 
form with such proof or verification as the Company may request.

ARTICLE 9.     NOTICES.

     All notices and other communications provided for or permitted hereunder 
shall be made in writing by hand delivery, registered first class mail, 
overnight courier, or telecopied, initially to the address set forth below, 
and thereafter at such other address, notice of which is given in accordance 
with the provisions of this ARTICLE 9.

     All notices to Holders are to be directed to each holder at such address 
as is listed for such Holder on the Register.

     All notices to the Company are to be directed to:

     Saliva Diagnostic Systems, Inc. 
     11719 NE 95th Street
     Vancouver, Washington 98682
     Attn:  Chief Executive Officer
     Telephone: (360) 696-4800
     Telecopier: (360) 254-7942

ARTICLE 10.    TIMES.

     Where this Debenture authorizes or requires the payment of money or the 
performance of a condition or obligation on a Saturday or Sunday or a public 
holiday, or authorizes or requires the payment of money or the performance of 
a condition or obligation within, before or after a period of time computed 
from a certain date, and such period of time ends on a Saturday or a Sunday 
or a public holiday, such payment may be made or condition or obligation 
performed on the next succeeding business day, and if the period ends at a 
specified hour, such payment may be made or condition performed, at or before 
the same hour of such next succeeding business day, with the same force and 
effect as if made or performed in accordance with the terms of this 
Debenture.  Where time is extended by virtue of the provisions of this 
ARTICLE 10, such extended time shall not be included in the computation of 
interest.


                                     -7-

<PAGE>

ARTICLE 11.    RULES OF CONSTRUCTION.

     In this Debenture, unless the context otherwise requires, words in the 
singular number include the plural, and in the plural include the singular, 
and words of the masculine gender include the feminine and the neuter, and 
when the sense so indicates, words of the neuter gender may refer to any 
gender.  The numbers and titles of articles and sections contained in this 
Debenture are inserted for convenience of reference only, and they neither 
form a part of this Debenture nor are they to be used in the construction or 
interpretation hereof. Wherever, in this Debenture, a determination of the 
Company is required or allowed, such determination shall be made by a 
majority of the Board of Directors of the Company and if it is made in good 
faith, it shall be conclusive and binding upon the Company and the Holder of 
this Debenture.

ARTICLE 12.    NATURE OF OBLIGATION; RANK.

     No provision of this Debenture shall alter or impair the obligation of 
the Company, which is absolute and unconditional, to pay the principal of, 
and interest on, this Debenture at the time, place, and rate, and in the coin 
or currency, herein prescribed.  This Debenture and all other Debentures now 
or hereafter issued of similar terms are direct obligations of the Company.  
This Debenture ranks equally with all other Debentures now or hereafter 
issued under the terms set forth herein.

ARTICLE 13.  GOVERNING LAW.

     The validity, terms, performance and enforcement of this Debenture shall 
be governed and construed by the provisions hereof and in accordance with the 
laws of the State of Delaware.

     IN WITNESS WHEREOF, the Company has duly executed this Debenture as of 
the date first written above.


                                       SALIVA DIAGNOSTIC SYSTEMS, INC.

                                       By:
                                          ------------------------------
(Corporate Seal)                       Name:
                                            ----------------------------
                                       Title:
                                             ---------------------------


                                     -8-

<PAGE>

                             NOTICE OF CONVERSION

          [To be completed and signed only upon conversion of Debenture]

     The undersigned, the Holder of this Debenture, hereby irrevocably elects 
to exercise the right to convert it into Common Stock, par value $.01 per 
share, of Saliva Diagnostic Systems, Inc. as follows:

[Complete if less than _________________________________ Dollars ($__________)*
all of ($1,000 or integral
multiples of $1,000)
principal amount 
is to be converted]


[Signature must be
guaranteed if          ________________________________________________________
registered holder      (Name of Holder of shares if different than registered
Holder of Debenture)
of stock differs
from registered        ________________________________________________________
Holder of              (Address of Holder of shares if different than address of
Debenture]              registered Holder of Debenture)


                       ________________________________________________________
                       (Social Security or EIN of Holder of shares if different 
                        than Holder of Debenture)

* If the principal amount of the Debenture to be converted is less than the 
entire principal amount thereof, a new Debenture for the balance of the 
principal amount shall be returned to the Holder of the Debenture.  All 
notices to be transmitted by hand delivery, facsimile or overnight courier.

Date:                         Sign:
     ----------------------        --------------------------------------------
                              (Signature must conform in all respects to name 
                              of Holder shown on face of the Debenture)

                              Print Name:
                                         --------------------------------------

                              Print Title, if applicable:
                                                         ----------------------


                                    -9-

<PAGE>

                           ASSIGNMENT OF DEBENTURE

The undersigned hereby sell(s) and assign(s) and transfer(s) unto

--------------------------------------------------------------------------------
                   (name, address and SSN or EIN of assignee)

                                                       Dollars ($              )
--------------------------------------------------------------------------------
    (principal amount of Debenture, $1,000 or integral multiples of $1,000)

of principal amount of the Debenture together with all accrued interest hereon.


Date:                         Sign:
     ----------------------        --------------------------------------------
                              (Signature must conform in all respects to name 
                              of Holder shown on face of Debenture)

                              Print Name:
                                         --------------------------------------

                              Print Title, if applicable:
                                                         ----------------------


                                     -10-