AMENDED AND RESTATED
             SENIOR SUBORDINATED SECURED CONVERTIBLE PROMISSORY NOTE

THESE  SECURITIES HAVE NOT BEEN REGISTERED  UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "ACT"),  NOR UNDER ANY STATE SECURITIES LAW AND SUCH SECURITIES MAY
NOT BE PLEDGED, SOLD, ASSIGNED, HYPOTHECATED, OR OTHERWISE TRANSFERRED UNTIL (1)
A REGISTRATION STATEMENT WITH RESPECT THERETO IS EFFECTIVE UNDER THE ACT AND ANY
APPLICABLE  STATE  SECURITIES  LAW OR (2) THE  COMPANY  RECEIVES  AN  OPINION OF
COUNSEL  TO THE  COMPANY OR  COUNSEL  TO THE  HOLDER OF SUCH  SECURITIES,  WHICH
COUNSEL  AND OPINION  ARE  REASONABLY  SATISFACTORY  TO THE  COMPANY,  THAT SUCH
SECURITIES MAY BE PLEDGED, SOLD, ASSIGNED,  HYPOTHECATED, OR TRANSFERRED WITHOUT
AN  EFFECTIVE   REGISTRATION  STATEMENT  UNDER  THE  ACT  AND  APPLICABLE  STATE
SECURITIES LAWS.

$_______                                                  Waltham, Massachusetts
                                                                    May __, 2000

     FOR VALUE RECEIVED, Hemagen Diagnostics,  Inc., a Delaware corporation with
offices at 34-40 Bear Hill Road,  Waltham,  Massachusetts 02451 (the "Company"),
and its subsidiary,  Reagents  Applications,  Inc. a Delaware  corporation  with
offices at 8225 Mercury Court, San Diego, California 92111,  (collectively,  the
"Obligors"), jointly and severally promise to pay to the order of_______________
and its  successors  and assigns (the  "Holder") at such place as the Holder may
designate by written notice to the Company, in lawful money of the United States
of America,  the sum of  _________________  dollars  ($______)  (the  "Principal
Amount")  plus all accrued  and unpaid  interest  on the  outstanding  Principal
Amount at the rate of eight  percent  (8%) per  annum.  The  Obligors  shall pay
accrued  interest on the  outstanding  Principal  Amount on a  quarterly  basis,
commencing June 30, 2000, and on payment of the Principal Amount. All principal,
premiums and interest are to be paid without setoff or counterclaim as set forth
below. The Company further agrees as follows:

Section 1.   Engagement Agreement.

     This  promissory  note (the  "Note") is being issued in  connection  with a
letter  agreement (the "Engagement  Agreement")  between the Company and Jesup &
Lamont  Securities  Corporation,  whereby  Jesup & Lamont  has  agreed to act as
placement  agent in connection  with a private  offering (the  "Offering")  of a
minimum of $4 million of units (the "Units"), each Unit consisting of a $500,000
Senior  Subordinated  Secured  Convertible  Note,  200,000  warrants to purchase
common stock (the  "Warrants")  and 93,750 shares of the Company's  common stock
(the "Common Stock").

Section 2.   Payments.

     (a) Unless this Note shall be converted in accordance  with the  provisions
of Section 7 or redeemed  earlier in  accordance  with Section 2(b) hereof,  the
Principal Amount, together with the redemption premium described below, shall be
due and payable on April 17, 2005.




     (b) At any time  after the  effective  date of the  registration  statement
covering  the shares of Common  Stock  included in the Units,  the Common  Stock
issuable  upon  conversion  of the  Note,  the  Warrants  and the  Common  Stock
underlying the Warrants,  upon 20 business days' notice to the Holder specifying
the date on which  payment is to be made,  the Obligors  shall have the right to
prepay  this  Note,  in full,  at any  time in an  amount  equal  to the  unpaid
Principal Amount plus all accrued but unpaid  interest.  If notice of prepayment
is  given  as  provided  above,  but the  Obligors  fail to  prepay  on the date
specified,  the Obligors shall be jointly and severally liable for the Principal
Amount,  plus all accrued  interest to the date specified plus default  interest
from the date specified, at the rate of 12% per annum until this Note is paid in
full.  Notice of  prepayment  having  been given,  this Note shall  nevertheless
continue to accrue interest and to be convertible until paid in full.

     (c) The  Obligors  and the Holder  intend  that this Note  comply  with any
applicable usury laws from time to time in effect. In furtherance  thereof,  the
Obligors  and  the  Holder  stipulate  and  agree  that  none of the  items  and
provisions  contained  in this Note shall be  construed  to create a contract to
pay, as consideration for the use,  forbearance or detention of money,  interest
at a rate in excess of the highest lawful rate under applicable law.

Section 3.  Representations, Warranties and Covenants of the Obligors.

     The Obligors represent, warrant and covenant to the Holder as follows:

     (a) Due  Organization,  etc. The Obligors are corporations  duly organized,
validly  existing,  and in good standing under the laws of the  jurisdiction  of
their incorporation or organization.

     (b)  Authority.  The  Obligors  have  all  requisite  corporate  power  and
authority  to own,  lease,  license and use their  properties  and assets and to
conduct the business in which they are engaged. The Obligors have full power and
authority to execute and deliver  this Note and to grant the  Security  Interest
(as defined  herein)  granted  herein,  and the  execution  and  delivery by the
Obligors of this Note, and the performance of their obligations  hereunder,  has
been duly  authorized by all necessary  corporate or other action.  This Note is
the legal, valid and binding obligation of the Obligors enforceable against them
in accordance with the terms hereof.

     (c) Qualification.  The Obligors are each duly licensed or qualified and in
good standing as a foreign  corporation in each jurisdiction  wherein the nature
of the business transacted by them or the nature of the property owned or leased
by them makes such licensing or  qualification  necessary,  the failure of which
would have a material adverse effect on the business, operations,  properties or
condition (financial or otherwise) of the Obligors.

     (d) Capitalization.  As of April 15, 2000, the Company's authorized capital
stock consisted of 30,000,000  shares of common stock,  $.01 par value per share
(the "Common Stock") and 1,000,000 shares of preferred stock, $.01 par value per
share, of which  approximately  8,259,790 shares of Common Stock were issued and
outstanding   (excluding   4,890,145   shares  issuable  upon  the  exercise  of
outstanding  options  and  warrants).  As of  April  15,  2000,  except  for the
Company's  2,900,281  outstanding  warrants  exercisable  at  $2.75  per  share,
1,989,864 shares issuable upon exercise of outstanding options at prices ranging
from $0.97 to $2.19 per share,  and the shares  issuable to the placement  agent





pursuant  to the  Offering,  there  were  no  other  outstanding  subscriptions,
options,  warrants rights,  pre-emptive rights or other contracts,  commitments,
undertakings  or  arrangements,  including  any right of  conversion or exchange
under any outstanding security,  promissory note, (other than Notes and Warrants
to be  issued  to  other  investors  in  the  Offering),  instrument  or  option
(collectively "Options "), obligating the Obligors to issue or sell any share of
its capital stock or grant, extend or enter into any Option.

     (e) No Dividends,  Redemptions. The Company will not (i) declare or pay any
dividend or make any other distribution on any equity securities of the Company,
except dividends or distributions payable in equity securities of the Company or
(ii)  purchase,  redeem or  otherwise  acquire  or retire  for value any  equity
securities of the Company.

     (f) Related Transactions.  The Obligors will not, without the prior written
consent  of  the  Majority  Holders  (as  hereinafter  defined),  engage  in any
transaction of any kind or nature with any affiliate of the Obligors unless such
transaction,  or in the case of a course of related or similar  transactions  or
continuing transactions, is or are upon terms which are fair to the Obligors, as
the case may be, and which are reasonably  similar to, or more beneficial to the
Obligors  than the terms  deemed  likely to occur in similar  transactions  with
unrelated persons under the same circumstances.

     (g) No Liens.  The Obligors shall not, without the prior written consent of
the Holders of at least a majority of the outstanding Principal Amount on all of
the Notes issued pursuant to the Offering  ("Majority  Consent") create,  incur,
assume or suffer to exist (collectively, "incur") any mortgage, pledge, security
interest, assignment, lien (statutory or other), claim, encumbrance of any kind,
license or sublicense or security interest (collectively, "Lien") in or upon any
of the  Collateral  (as  defined  herein),  except  for  (1)  liens  for  taxes,
assessments or similar charges  incurred in the ordinary course of business that
are not yet due and  payable;  (2)  statutory  Liens of  landlords  and Liens of
carriers,  warehousemen,  mechanics,  materialmen and other Liens imposed by law
incurred in the  ordinary  course of business for sums not yet  delinquent,  (3)
Liens incurred or deposits made in the ordinary course of business in connection
with  workers'  compensation,  unemployment  insurance and other types of social
security,  (4)  easements,  rights-of-way,   encroachments,  leases,  royalties,
restrictions and other similar title exceptions or encumbrances provided such do
not,  in the  aggregate,  materially  interfere  with the  ordinary  conduct  of
business of Obligors or materially reduce or impair the value of the real estate
so encumbered,  (5) Liens granted to the Holders of Notes issued pursuant to the
Offering,  (6)  Liens  securing  any  conditional  sales  agreements,   security
agreements,  equipment  leases in the nature of title  retention  agreements  or
security agreements or other similar title retention  agreements entered into by
Obligors  on,  prior to the date  hereof  or after  the date  hereof in order to
secure the payment of the purchase price of any equipment  purchased,  leased or
otherwise  acquired by Obligors for use in the  ordinary  course of its business
having  aggregate cost of less than $100,000,  (7) Liens granted to (i) a lender
pursuant to or with respect to a revolving  credit  facility of up to $1 million
to be entered  into by the  Obligors,  or (ii) secure  indebtedness  incurred by
Obligors if the proceeds of which are used to prepay any Note issued pursuant to
the Offering,  which such  indebtedness  shall be senior in right of payment and
preference  to this Note  ("Take-out  Indebtedness  ") and (8)  Liens  listed on
Schedule 3(p) hereof.




     (h)  Indebtedness.  Except  for  the  indebtedness  incurred  to  financial
institutions and other individuals listed and described on Schedule 3(h) annexed
hereto,  the Obligors do not have any outstanding  indebtedness  (outside of the
ordinary course of business).  The Obligors shall not at any time create,  incur
or assume,  or become or be liable in respect of, any  indebtedness,  other than
(1)  indebtedness  arising  under  this Note and the other  notes  issued in the
Offering,  (2) extensions of trade debt in the ordinary course of business,  (3)
indebtedness  secured by Liens  permitted  by  Section  3(g),  (4)  subordinated
indebtedness other than the existing  subordinated  indebtedness as described on
Schedule  3(h)  annexed  hereto in an aggregate  principal  amount not to exceed
$4,000,000  at any  one  time  outstanding  for  the  purpose  of  financing  an
acquisition by an Obligor of the business of another person.

     (i)  Maintenance of  Collateral.  The Obligors will maintain the Collateral
(as hereinafter defined) in good operating condition and repair.

     (j) Sale or Disposition.  The Obligors will not sell,  contract for sale or
otherwise  dispose of any of the  Collateral or any interest  therein  except as
provided in paragraph (t) in this Section 3.

     (k) Taxes. The Obligors will pay promptly when due all taxes due from them,
except for taxes and assessments which are being contested in good faith.

     (l) Further  Assurances.  The Obligors will promptly execute and deliver to
the  placement  agent of the  offering as agent for the Holders  such  financing
statements,  certificates,  notices and other documents or instruments as may be
necessary to enable the placement agent to perfect or from time to time perfect,
renew or continue the Security  Interest  granted  herein for the benefit of the
Holders of the Notes, including,  without limitation, such financing statements,
certificates  and other  documents  as may be  necessary  to  perfect a security
interest in any additional  Collateral  hereafter acquired by the Obligors or in
any replacements or proceeds  thereof.  The Obligors hereby authorize  placement
agent to take all  action  (including,  without  limitation,  the  filing of any
Uniform  Commercial Code Financing  Statements or amendments thereto without the
signature of the Obligors or the  notification  of any account  debtor or payor)
that Holder may deem necessary or desirable to perfect or otherwise  protect the
Security Interest described hereunder and to obtain the benefits of this Note.

     (m) No  Conflict.  Except as  provided  on  Schedule  3(m) which is annexed
hereto, the Obligors are not in default under any indenture,  mortgage,  deed of
trust,  agreement or other instrument to which they or either of them is a party
or by which they or any of their assets may be bound; and (ii) the execution and
delivery  of this  Note and  compliance  with the  provisions  hereof  shall not
violate any  provision of law  applicable  to the  Obligors;  nor shall the same
conflict  with  or  result  in a  breach  of  any of the  terms,  conditions  or
provisions of, or constitute a default under,  the certificate of  incorporation
or by-laws of either of the Obligors, or result in the breach of, constitute any
default under, or conflict with the terms of any indenture,  mortgage, agreement
or other  instrument  to which the Obligors are party or by which they or any of
their  assets may be bound or result in the creation or  imposition  of any Lien
upon  any of the  Collateral,  other  than  for the  Security  Interest  granted
pursuant to the Notes issued in connection with the Offering.




     (n)  Consents.   No  consent,   approval,   order,   authorization  of,  or
registration,  qualification or filing with, any  governmental  authority or any
other  party is  required on the part of the  Obligors  in  connection  with the
execution  and  delivery of this Note,  the  granting of the  Security  Interest
granted  herein,  and  the  performance  and  consummation  of the  transactions
contemplated  hereby,  other than (i) such  consents that have been obtained and
(ii) the  filing  of any  financing  statement  or  similar  instrument  that is
required to perfect Holder's Security Interest.

     (o) Litigation.  There are no suits,  proceedings or investigations pending
or, to the Obligors' knowledge, threatened, against either of the Obligors which
questions the validity of this Note or which,  individually or in the aggregate,
if determined adversely,  would have a material adverse effect on the Collateral
or the  business,  operation or condition  (financial or otherwise) of either of
the Obligors.

     (p) Title. Except as otherwise disclosed in Schedule 3(p) which is attached
hereto,  the  Obligors  are the sole  owners  of,  and have good  title to,  the
Collateral, free and clear of any Lien, except for the Security Interest granted
hereby and there is no financing  statement or similar filing now on file in any
public office covering any material part of the Collateral.

     (q) Locations.  The chief  executive  offices of the Obligors is located at
the  addresses set forth above.  All  inventory  and equipment  held on the date
hereof by the Obligors is located at one of the locations shown on Schedule 3(q)
hereto.

     (r) Use of  Proceeds.  The  Obligors  shall  use the  proceeds  of the loan
evidenced by this Note solely to repay its existing bank  indebtedness,  and all
accrued unpaid interest  thereon of  $3,896,140.27,  owed to Fleet National Bank
(the "Fleet Credit Line") and for general working capital purposes.  In no event
shall any portion of the proceeds of the loan  evidenced  hereby be used for the
repayment of any indebtedness of the Obligors other than the Fleet Credit Line.

     (s) Ordinary Course.  While all or any portion of this Note is outstanding,
the Obligors shall conduct their operations  according to the ordinary and usual
course of the business  consistent with past practice,  to preserve intact their
present business  organization and structure,  to keep available the services of
their present  officers,  agents and  employees,  to preserve and maintain their
assets and the goodwill of the business and to preserve their relationships with
employees,  customers and others having  business  dealings with them and not to
enter into,  amend,  modify,  terminate,  renew,  extend,  or waive any existing
material right under any material agreements of the Obligors.

     (t)  Limitation on  Disposition  of Assets.  No Obligor shall sell,  lease,
transfer or otherwise dispose of any of its property, business, assets or shares
of  capital  stock or other  equity  securities  in a  subsidiary,  except to an
Obligor,  except  for bona fide sales of  inventory  in the  ordinary  course of
business  and  dispositions  of obsolete  equipment  in the  ordinary  course of
business, unless (1) the consideration received is in cash and at least equal to
the fair market value of such assets or (2) the aggregate market value of assets
sold or otherwise  disposed of in any series of transactions does not exceed One
Hundred Thousand Dollars ($100,000).




     (u) Subsequent Transactions. Notwithstanding Section 2(b), while all or any
portion of this Note is outstanding, the Obligors shall:

          (i) use 50% of the net proceeds from funds  received by either or both
     of the  Obligors  from the  exercise of  outstanding  options or  warrants,
     provided such funds, in the aggregate, exceed $1 million;

          (ii) use 100% of the net proceeds from all sales of assets  (excluding
     sales of  inventory  and  obsolete  equipment  in the  ordinary  course  of
     business) exceeding $100,000, at fair market value and for cash; and

          (iii) 50% of the net proceeds  from the sale of [Raichem]  received by
     either or both of the Obligors to reduce the outstanding  Principal  Amount
     and accrued and unpaid  interest  due on the Notes held by investors in the
     Offering on a pro rata basis.

     Any reduction in Principal Amount or the accrued and unpaid interest on the
Notes made pursuant to this Section 3(u) shall be made on or before the 30th day
after the date Company receives any funds listed above.

     Notwithstanding  the  foregoing,  all secured  debt raised by the  Obligors
subsequent  to the date hereof shall be used to repay the  Principal  Amount and
accrued and unpaid interest on the Note,  provided,  however,  that the Obligors
shall  not be  obligated  to use any  portion  of any  secured  debt of up to $1
million that is raised by Obligors in connection with a revolving credit line.

     (v)  Reports.  The Common  Stock of the Company is  registered  pursuant to
Section 12(g) of the Securities  Exchange Act of 1934, as amended (the "Exchange
Act"), and the Company has filed all reports and other documents  required to be
filed  by it  with  the  Securities  and  Exchange  Commission  pursuant  to the
reporting  requirements  of the Exchange  Act. The  Obligors  covenant  that the
Company shall file such reports and other  documents  required to be filed by it
with the  Securities  and Exchange  Commission  on a timely  basis,  and it will
provide the  placement  agent of the  Offering and the Holders of the Notes with
copies of such reports and other documents,  until such time as the later of the
repayment,  in full,  of all of the  Principal  Amount  and  accrued  and unpaid
interest  thereon,  or  the  sale  of  all of the  Common  Stock  issuable  upon
conversion of the Notes.

     (w) Reservation of Common Stock.  There have been reserved and the Obligors
shall at all times keep  reserved,  out of the  authorized  but unissued  Common
Stock of the Company free from any preemptive rights, rights of first refusal or
other  restrictions  (other  than  pursuant  to the Act),  a number of shares of
Common  Stock  sufficient  to provide  for the rights of Holders to convert  the
Notes.  Once  delivered  upon valid  conversion of the Notes,  any shares of the
Common Stock will be valid,  fully-paid and non-assessable.  The transfer agent,
if any, for the Common Stock, and every subsequent transfer agent for any Common
Stock  issuable  upon the exercise of any of the rights of conversion as set out
in this Note,  shall be  irrevocably  authorized  and  directed  at all times to
reserve such number of  authorized  Common Stock as shall be requisite  for such





purpose.  The Obligors  shall keep a copy of this Note on file with any transfer
agent for the Common  Stock and with  every  subsequent  transfer  agent for the
Common Stock issuable upon the exercise of the rights of conversion  represented
by this Note. Any transfer agent for the Common Stock and any successor transfer
agent for the  Common  Stock is  hereby  irrevocably  authorized  to cause to be
issued from time to time the share certificates required to honor this Note upon
its  conversion in accordance  with the terms hereof.  The Obligors shall supply
any such transfer agent with duly executed share certificates for such purpose.

Section 4.   Security Interest.

     (a) Subject to paragraph  (b) in this Section 4, the Obligors  hereby grant
to the Holder a first priority  security  interest in and lien on (the "Security
Interest")  the Collateral to secure  performance  and payment of (i) this Note,
and (ii) all  other  obligations  and  indebtedness  of the  Obligors  to Holder
hereunder, of whatever kind and whenever or however created or incurred, whether
absolute or  contingent,  matured or  unmatured,  direct or indirect (all of the
foregoing  being the  "Secured  Indebtedness").  The Security  Interest  granted
herein shall  continue in full force and effect until,  and Holder shall release
the Security Interest when, all of the Secured  Indebtedness has been discharged
or converted into Common Stock in accordance with the terms hereof.

     (b) The Secured  Indebtedness  shall be secured by the Security Interest in
the Collateral,  and shall be senior to all other  indebtedness of the Obligors.
Notwithstanding the foregoing, the Security Interest shall be subordinate to (i)
the Security  Interest on any  Collateral  granted in connection  with the Fleet
Credit  Line;  (ii) one  revolving  line of bank credit that is equal to or less
than $1  million,  and (iii)  any  secured  financing  that is  greater  than $2
million,  provided  that (A) the Obligors  provide the Holder 20 business  days'
written  notice of such  secured  financing,  and (B) all of the funds raised in
connection with such secured  financing  shall be used to reduce,  on a pro rata
basis, the Principal Amount and accrued and unpaid interest owed on the Notes.

     (c) As used herein, the term "Collateral" shall mean and include all of the
Obligors' right, title and interest in and to all real,  tangible and intangible
property of the Obligors  whether now or hereafter  existing,  of every kind and
description,  now owned or  hereafter  acquired  and  wherever  located  and the
proceeds (including any insurance  proceeds),  products and accessions of and to
any thereof,  and all books and records pertaining to all of the foregoing,  all
of which are and shall at all times be and remain, free and clear of any and all
Liens  except for any Lien in  connection  with the  indebtedness  listed in the
second sentence of Section 4(b).

Section 5.   Events of Default.

     It shall be an event of default  ("Event of Default")  with respect to this
Note upon the occurrence and, where applicable,  continuation uncured, of any of
the following events:

     (a) Default in Payment, etc.

          (i) a  default  in the  payment  of (A) the  Principal  Amount  or (B)
     quarterly  interest payment on this Note, when and as the same shall become
     due  and  payable,  either  by the  terms  hereof  or  upon  redemption  or



     otherwise,  which default in the case of clause (B) of this Section 5(a)(i)
     shall continue  uncured for a period of seven (7) days after receipt by the
     Obligors of written notice of such default; or

          (ii) a default in the performance,  or breach, of any  representation,
     warranty or  covenant of the  Obligors in this Note and (to the extent such
     default or breach can be cured) the  continuance  of such default or breach
     uncured  for a period of seven (7) days after  receipt by the  Obligors  of
     written notice as to such breach.

     (b) Bankruptcy,  Insolvency, etc. Either of the Obligors becoming insolvent
(however  defined  or  evidenced)  or the  entry of a decree or order by a court
having jurisdiction  adjudging either of the Obligors bankrupt or insolvent,  or
approving  a  petition  seeking  reorganization,   arrangement,  adjustment,  or
composition  of or in respect of either of the Obligors,  under federal or other
applicable  bankruptcy  law,  as  now or  hereafter  constituted,  or any  other
applicable federal or state bankruptcy, insolvency, dissolution,  liquidation or
other similar law, or the  commencement by either of the Obligors of a voluntary
case under  federal or other  applicable  bankruptcy  law,  as now or  hereafter
constituted,  or any other applicable  federal or state bankruptcy,  insolvency,
dissolution,  liquidation  or other similar law, or the consent by either of the
Obligors  to  the  institution  of  bankruptcy,   dissolution,   liquidation  or
insolvency proceedings against it, or the filing by either of them of a petition
or answer or consent  seeking  reorganization  or relief under  federal or other
applicable  bankruptcy law or any other applicable federal,  state or other law,
or the  consent  by either  of them to the  filing  of such  petition  or to the
appointment  of a receiver,  liquidator,  assignee,  trustee,  sequestrator,  or
similar  official,  of  either of them or of any  substantial  part of either of
their property, or the making by either of them of an assignment for the benefit
of creditors,  or the admission by either of them in writing of the inability to
pay their debts generally as they become due, or the taking of corporate  action
by either of the Obligors in furtherance of any such action.

     (c) Involuntary Bankruptcy.  A proceeding or case being commenced,  without
the  application  or  consent  of one or more of the  Obligors  in any  court of
competent   jurisdiction,   seeking   (i)   its   reorganization,   liquidation,
dissolution,  arrangement or winding-up,  or the  composition or readjustment of
its debts,  (ii) the appointment of a receiver,  custodian,  trustee,  examiner,
liquidator or the like of such Obligor, or of all or any substantial part of its
property  or (iii)  similar  relief in  respect  of such  Obligor  under any law
relating to bankruptcy, insolvency,  reorganization,  winding-up, or composition
or adjustment of debts, and such proceeding or case continuing  undismissed,  or
an order,  judgment or decree  approving or ordering any of the foregoing  being
entered and continuing  unstayed and in effect, for a period of 60 or more days;
or an order for relief  against one or more of the Obligors  being entered in an
involuntary case under the U.S. Bankruptcy Code.

     (d) Default on Other  Indebtedness.  The default in payment of principal of
or interest on any other indebtedness for borrowed money owed by the Obligors or
default in the performance or observance of the terms of any instrument pursuant
to which such  indebtedness was created or secured,  the effect of which default
is to cause any holder of any such indebtedness to cause, or (with the giving of
any  notice or the lapse of any time) to permit  the  holder or  holders of such
indebtedness  to cause the same to become  due or  prepaid  in full prior to its
stated maturity.





Section 6.  Remedies Upon Default.

     (a) Acceleration and Penalty  Interest.  Upon an Event of Default specified
in Section  5(a),  Section  5(c) or  Section  5(d),  and at any time  during the
continuation  thereof, the Holder, by notice given to the Obligors,  may declare
the entire unpaid Principal Amount,  and, if applicable,  redemption premium, of
this Note then outstanding to be due and payable immediately,  and upon any such
declaration the same shall, together with accrued interest thereon and all other
obligations  of the  Obligors  accrued  hereunder  and  under  the  Subscription
Agreement, without presentment, demand, protest or other notice of any kind, all
of which are hereby waived by each Obligor.  Upon an Event of Default  specified
in Section  5(b),  the entire  unpaid  Principal  Amount,  and,  if  applicable,
redemption premium, of this Note then outstanding shall automatically become due
and payable  immediately,  together with accrued  interest thereon and all other
obligations  of the  Obligors  accrued  hereunder  and  under  the  Subscription
Agreement,  without presentment,  demand,  protest or notice of any kind, all of
which  are  hereby  waived by each  Obligor.  After  acceleration  and until the
Principal  Amount and all accrued and unpaid  interest is paid  pursuant to this
Section 6(a),  interest shall accrue on the unpaid  Principal  Amount and on the
accrued  and unpaid  interest  on the Note up to and  including  the date of the
Event of Default at the rate of 12% per annum.

     (b) Remedies Regarding Security Interest in Collateral. Upon the occurrence
of any  Event of  Default,  the  Holder,  together  with  Holders  of at least a
majority of the Principal  Amount of Notes issued  pursuant to the Offering (the
"Majority  Holders")  shall have the following  additional  rights and remedies,
provided  such rights and  remedies  shall be enforced on behalf of the Majority
Holders  solely by a  representative  (the  "Representative")  of Jesup & Lamont
Securities  Corporation,  such Representative to be identified by written notice
to the Obligors:

          (i) All  rights  and  remedies  provided  by law,  including,  without
     limitation,  those provided by the Uniform  Commercial Code as in effect in
     the State of Massachusetts from time to time (the "UCC").

          (ii) The right to take  possession of the Collateral  and, in addition
     thereto,  the right to enter upon any premises on which the  Collateral  or
     any part  thereof  may be  situated,  without  notice,  and remove the same
     therefrom.  Representative  may require the Obligors to make the Collateral
     (to the extent the same is moveable)  available to the  Representative at a
     place to be designated by the Representative which is reasonably convenient
     to both parties at the Obligors' expense.  Unless the Collateral  threatens
     to  decline  speedily  in  value  or is of a  type  customarily  sold  on a
     recognized market,  the Representative  will give the Obligors at least two
     (2) days' prior  written  notice at the address of the  Obligors  set forth
     above (or at such other address or addresses as the Obligors  shall specify
     in writing to the  Representative) of the time and place of any public sale
     thereof or of the time after which any private  sale or any other  intended
     disposition  thereof is to be made. Any such notice shall be deemed to meet
     any  requirement  hereunder or under any applicable law (including the UCC)
     that reasonable notification be given of the time and place of such sale or
     other  disposition.  After  deducting all costs and expenses of collection,
     storage,  custody,  sale  or  other  disposition  and  delivery  (including
     reasonable legal costs and attorneys' fees, expenses and disbursements) and
     all other reasonable charges against the Collateral, the remaining proceeds




     of any such sale or  disposition  shall be  applied  to the  payment of the
     Secured  Indebtedness in such order of priority as the Representative shall
     determine  and any  surplus  shall be  returned  to the  Obligors or to any
     person or party lawfully entitled thereto. In the event the proceeds of any
     sale,  lease  or  other   disposition  of  the  Collateral   hereunder  are
     insufficient  to pay all of the Secured  Indebtedness in full, the Obligors
     will be liable for the  deficiency,  together with interest  thereon at the
     highest rate of interest  provided in this Note, and the costs and expenses
     of collection  of such  deficiency,  including (to the extent  permitted by
     law),  without  limitation,   reasonable   attorneys'  fees,  expenses  and
     disbursements.

     (c)  Proceedings  and  Actions.  During  the  continuation  of any Event of
Default,  the Holder may institute such actions and proceedings in law or equity
as it shall deem  expedient  for the  protection of its rights and may prosecute
and enforce its claims  against all assets of the  Obligors,  and in  connection
with any such  action  or  proceeding  shall be  entitled  to  receive  from the
Obligors  payment  of the  Principal  Amount of this Note plus any  accrued  and
unpaid interest,  to the date of payment plus reasonable  expenses of collection
including,  without  limitation,  reasonable  attorneys' fees and expenses.  All
rights and remedies  available to the Holder  pursuant to the provisions of this
Note,  applicable  law and  otherwise  are  cumulative,  not  exclusive  and are
enforceable alternatively and/or concurrently.

Section 7.   Conversion of the Note.

     At  the  option  of the  Holder,  all or  any  portion  of the  outstanding
Principal  Amount,  plus all accrued and unpaid  interest on the Note,  shall be
convertible into shares of Common Stock at a conversion price of $2.50 per share
(the  "Conversion  Price"),  provided,  that the Holder  shall  not,  on any one
occasion,  convert  an amount  that is less than  $25,000.  On the last day (the
"Reset Date") of the sixth month following the effectiveness of the registration
statement  (the  "Registration  Statement")  that is to be filed by the Obligors
covering  the shares of Common  Stock issued as part of the Units and the Common
Stock issuable upon conversion of the Notes underlying the Units, the Conversion
Price shall be adjusted to equal the lesser of (i) the Conversion  Price or (ii)
the  average  closing  bid price for the Common  Stock as reported by the Nasdaq
SmallCap  Market for the twenty trading days prior to the Reset Date;  provided,
however,  that the  adjusted  Conversion  Price shall not be less than $2.00 per
share.

     Notwithstanding  the  foregoing,   if  after  the  effective  date  of  the
Registration  Statement  (the  "Effective  Date") the  closing bid price for the
Common Stock, as reported by the Nasdaq SmallCap Market,  has exceeded $4.50 for
ten consecutive  trading days, the Obligors,  at its sole  discretion,  upon ten
days  written  notice to the  Holder,  may  require  the Holder to  convert  the
outstanding  Principal Amount,  plus all accrued and unpaid interest on the Note
at the Conversion  Price in effect on the date of such  conversion  (the "Forced
Conversion").  The officers,  directors and  affiliates of the Obligors who have
purchased  units in the Offering and are Holders of Notes (the "D&O  Investors")
shall only be  subject to a Forced  Conversion  to the extent  that such  Forced
Conversion  does not cause a "short  swing  profit"  violation  as  provided  in
Section 16(b) of the Securities Exchange Act of 1934.

     Pursuant to a Subscription Agreement,  dated of even date herewith, between
the Holder and the  Obligors,  the  Obligors  agree to use their best efforts to
file the Registration Statement,  within 45 days of the closing of the Offering,




relating to the Common Stock included in the Units and the Common Stock issuable
upon  conversion  of this Note.  In the  Subscription  Agreement,  the  Obligors
covenant to the Holder to cause such Registration  Statement to become effective
within 120 days of the closing of the Offering.  The Obligors have agreed to pay
the Holder a penalty  equal to one percent (1%) of the  Principal  Amount of the
Note per month for (i) each month after the 45 day period  listed above that the
registration  has not been filed with the S.E.C.;  and (ii) each month after the
120 day  period  listed  above  that  the  registration  statement  has not been
declared  effective,  provided,  that the Company  shall not be obligated to pay
more than 10% of the Principal Amount per annum.

     In the event of a split,  subdivision or combination or similar transaction
in the Company's  Common Stock, or the issuance of a dividend  consisting of the
Company's Common Stock, the Conversion Price shall be  proportionally  increased
or  decreased,  as  the  case  may  be.  Additionally,   in  the  event  of  any
reclassification,  consolidation,  merger  or sale of  substantially  all of the
Company's assets or similar transaction, the Holder shall be entitled to receive
upon conversion the kind and number of shares of stock and other  securities and
property receivable upon such transaction as if the Holder were the owner of the
Common  Stock  issuable  hereunder  immediately  prior to any such  event at the
Conversion Price in effect on the date of the closing of such transaction.

Section 8.   Restrictions on Transfer.

     The Holder  acknowledges  that it has been advised by the Company that this
Note,  or the  shares of Common  Stock  issuable  upon  conversion  of this Note
(collectively,  the "Securities")  have not been registered under the Securities
Act of 1933, as amended (as amended,  the "Act"),  that the Securities are being
issued on the basis of the statutory  exemption  provided by section 4(2) of the
Act and/or  Regulation D promulgated  thereunder  relating to transactions by an
issuer not involving any public offering.  The Holder  acknowledges  that it has
been informed by the Company of, or is otherwise  familiar  with,  the nature of
the limitations  imposed by the Act and the rules and regulations  thereunder on
the  transfer of  Securities.  In  particular,  the Holder  agrees that no sale,
assignment,  or transfer of the Securities shall be valid or effective,  and the
Obligors shall not be required to give any effect to any such sale,  assignment,
or transfer,  unless (i) the sale, assignment,  or transfer of the Securities is
registered  under  the Act,  it being  understood  that the  Securities  are not
currently  registered  under the Act and that the Obligors have no obligation or
intention to register the Note, or (ii) the  Securities are sold,  assigned,  or
transferred in accordance with all the  requirements and limitations of Rule 144
under the Act, it being understood that Rule 144 is not available at the present
time for the sale of the Note and that there can be no  assurance  that Rule 144
sales  will be  available  at any  time  in the  future,  or  (iii)  such  sale,
assignment, or transfer is otherwise exempt from registration under the Act. The
Holder and each transferee hereof further agrees that if any distribution of the
Securities  is  proposed  to be made by them  otherwise  than by  delivery  of a
prospectus  meeting the requirements of Section 10 of the Act, such action shall
be taken only  after  submission  to the  Obligors  of an  opinion  of  counsel,
reasonably  satisfactory in form and substance to the Obligors' counsel,  to the
effect that the proposed  distribution will not be in violation of the Act or of
applicable  state law.  Furthermore,  it shall be a condition to the transfer of
the Note  that  any  transferee  thereof  deliver  to the  Company  his  written
agreement to accept and be bound by all of the terms and conditions contained in
this Note.




Section 9.   Miscellaneous.

     (a) This Note may be altered only by prior written  agreement signed by the
party against whom enforcement of any waiver, change, modification, or discharge
is sought. This Note may not be modified by an oral agreement, even if supported
by new consideration.

     (b) Notwithstanding  anything provided herein,  Holder may assign this Note
in  whole  or in  part  to one or more  officers  or  partners  of  Holder.  The
obligations  under this Note may not be  assigned  by the  Obligors  without the
prior  written  consent of the Holder (or all of the  Holders).  The  covenants,
terms  and  conditions  contained  in this  Note  apply to and  bind the  heirs,
successors, executors, administrators and assigns of the parties.

     (c) Upon receipt by the Obligors of evidence reasonably satisfactory to the
Obligors of the loss,  theft,  destruction  or mutilation  of this Note,  and of
indemnity  or  security  reasonably  satisfactory  to  the  Obligors,  and  upon
reimbursement to the Obligors of all reasonable expenses incidental thereto, and
upon surrender and  cancellation  of this Note, if mutilated,  the Obligors will
make and  deliver a new Note of like  tenor and of the same  series,  in lieu of
this Note.

     (d) This Note constitutes a final written expression of all of the terms of
the agreement  between the parties  regarding  the subject  matter  hereof,  and
supersedes all prior agreements, understandings, and representations between the
parties (except the Engagement  Agreement,  the  Subscription  Agreement and the
Warrant Agreement). If any provision or any word, term, clause, or other part of
any  provision  of this Note shall be invalid for any reason,  the same shall be
ineffective,  but the  remainder  of this Note shall not be  affected  and shall
remain in full force and effect.

     (e) This Note shall be governed by and  construed  in  accordance  with the
laws of the State of New York  without  giving  effect to its  conflicts  of law
principles.  The Company agrees that any dispute or  controversy  arising out of
this Note shall be  adjudicated  in a court located in New York City, and hereby
submits  (on  its  behalf  and  on  behalf  of   Subsidiary)  to  the  exclusive
jurisdiction  of the courts of the State of New York  located  in New York,  New
York,  and of the  federal  courts in the  Southern  District  of New York,  and
irrevocably  waives any  objection it now or hereafter may have  respecting  the
venue of such action or  proceeding  brought in such a court or  respecting  the
fact that such court is an  inconvenient  forum,  and consents to the service of
process in any such action or  proceeding  by means of  registered  or certified
mail, return receipt requested, to the address set forth below.

     (f) All notices,  consents,  or other  communications  provided for in this
Note or  otherwise  required by law shall be in writing and  delivered  by first
class mail,  and will be deemed to have been given or delivered on the date such
notice,  purchase price or other  communication is so delivered,  and, if to the
Company,  it will be addressed  to the address  specified  above,  and if to the
Holder,  it will be  addressed  to the  registered  Holder at his  address as it
appears on the books of the Corporation.

     Such  addresses  may be  changed  by  notice  given  as  provided  in  this
subsection.  Notices  shall be  effective  upon the date of  receipt;  provided,
however,  that a notice (other than a notice of a changed address) sent by first
class mail shall be  presumed  received  no later than three (3)  business  days
following the date of sending.







IN WITNESS WHEREOF,  the Company has executed this Note effective as of the date
first set forth above.

                            HEMAGEN DIAGNOSTICS, INC.



                            By:_________________________________
                               Name:
                               Title:

                           REAGENTS APPLICATIONS, INC.



                            By:_________________________________
                               Name:
                               Title:






                              NOTE CONVERSION FORM

To:  Hemagen Diagnostics, Inc. and Reagents Applications, Inc.

         The undersigned irrevocably elects to convert:

                           [  ]     ALL, or
                           [  ]     $_____________

of the accrued and unpaid interest and principal owed on the Senior Subordinated
Secured  Convertible  Promissory Note (the "Note") which is attached hereto. The
undersigned  requests that the  certificates  representing  the shares of common
stock as to which  this Note is being  converted  (the "  Conversion  Shares")be
registered  as follows and requests  Hemagen  Diagnostics,  Inc. to so cause the
registration thereof:

Name:__________________________________________________________________________
Social Security or Employer Identification Number:_____________________________
Address:_______________________________________________________________________
Deliver to:____________________________________________________________________
Address:_______________________________________________________________________

     If only a portion of the principal  amount and accrued and unpaid  interest
owed on the Note is  converted,  please  issue a new Note for the balance of the
unpaid  principal amount and accrued and unpaid interest owed on the Note to the
registered  holder  thereof and deliver it to the  undersigned  at the following
address:

Address:_________________________________________________________________


Date:  _______________, 20 __

         _________________________________________________
         (Signature must conform to the name of the holder
         of the Note specified on the face of the Note)








                                  SCHEDULE 3(h)

                              EXISTING INDEBTEDNESS

Fleet Bank  Boston  Revolving  Line of Credit,  Balance as of April 17, 2000 was
$3,896,540.27

Dade Behring,  Inc.  Unsecured  Promissory  Note in the amount of $1,250,000 due
September 1, 2000.








                                  SCHEDULE 3(m)

                             DEFAULT OF INDEBTEDNESS

The Company was in default of its  Financial  Covenants  regarding the Revolving
Line of Credit as of April 14,  2000.  On March 1,  2000  Fleet  BankBoston  and
Hemagen Diagnostics,  Inc, Reagents Applications,  Inc. and Hemagen Diagnosticos
Commercio Importacao E Exportacao Ltd., the obligors, entered into a Forbearance
Agreement.  In the March 1, 2000 Agreement,  Fleet BankBoston agreed to forebear
from making demand upon the obligors and/or otherwise  exercise its rights under
the loan document upon default until March 31, 2000. This Forbearance  Agreement
was subsequently extended to April 14, 2000.







                                  SCHEDULE 3(q)

                        LOCATION OF INVENTORY & EQUIPMENT

Hemagen Diagnostics, Inc.
40 Bear Hill Road
Waltham, Massachusetts 02451

Hemagen Diagnostics, Inc.
Virgo Products Division
9033 Red Branch Road
Columbia, Maryland 21045

Hemagen Diagnostics, Inc.
Reagents Applications, Inc.
8225 Mercury Court
San Diego, California 92111

Hemagen Diagnostics, Inc.
c/o Hemagen Diagnosticos Commercio Importacao E Exportacao Ltd.
Rua Tavares Cabral, 185
Sao Paulo - SP - CEP 05423-030, Brazil

Hemagen Diagnostics, Inc.
c/o Dade Behring, Inc.
Building 100
Route 896
Newark, Delaware 19714-6101






                                  SCHEDULE 3(p)
                           LIENS AND TITLE EXCEPTIONS


Secured Party                  Date Filed    File Number            Collateral
- --------------------------------------------------------------------------------
                            Hemagen Diagnostics, Inc.
                           Delaware Secretary of State
- --------------------------------------------------------------------------------
BankBoston, NA                 8-31-98       9839480*               Blanket Lien
- --------------------------------------------------------------------------------
                            Hemagen Diagnostics, Inc.
                             Fulton County, Georgia
- --------------------------------------------------------------------------------
BankBoston, NA                 9-3-99        60199917302*           Blanket Lien
- --------------------------------------------------------------------------------
                            Hemagen Diagnostics, Inc.
                 Maryland Department of Assessment and Taxation
- --------------------------------------------------------------------------------
BankBoston, NA                 10-28-98      39133021*              Blanket Lien
- --------------------------------------------------------------------------------
                            Hemagen Diagnostics, Inc.
                        Massachusetts Secretary of State
- --------------------------------------------------------------------------------
The  First  National           7-27-95       328246*  Certificate  of Deposit
Bank of Boston                                        Account #1944-65658 and
                                                      1994-65661 including any
                                                      rollovers, cash and pro-
                                                      ceeds including insurance,
                                                      general intangibles and
                                                      accounts proceeds
- --------------------------------------------------------------------------------
The  First  National           1-16-96       363205*  Certificate  of Deposit
Bank of Boston                                        Account # 1944-65658 and
                                                      1994-65661  including  any
                                                      rollovers,  cash  and pro-
                                                      ceeds including insurance,
                                                      general  intangibles  and
                                                      accounts proceeds
- --------------------------------------------------------------------------------
LaSalle National Bank          8-12-97       489516   Specific lab equipment and
                                                      attachments  and  acces-
                                                      sories. True rental not
                                                      intended as security.
- --------------------------------------------------------------------------------
BankBoston, NA                 8-31-98       574833*                Blanket Lien
- --------------------------------------------------------------------------------
BankBoston, NA                 8-31-98       574834*                Blanket Lien
- --------------------------------------------------------------------------------
Boston  Private  Bank          9-1-98        575048   specific leased equipment
& Trust Company
- --------------------------------------------------------------------------------
                            Hemagen Diagnostics, Inc.
                                 Town of Waltham
                           Through Date March 21, 2000
- --------------------------------------------------------------------------------
The  First  National           7-27-95       49350*   Certificate  of Deposit
Bank of Boston                                        Account # 1944-65658 and
                                                      1994-65661  including  any
                                                      rollovers, cash and pro-
                                                      ceeds including insurance,
                                                      general   intangibles and
                                                      accounts proceeds
- --------------------------------------------------------------------------------
The  First  National           1-17-96       49830*   Certificate  of Deposit
Bank of Boston                                        Account # 1944-65658 and
                                                      1994-65661  including  any
                                                      rollovers, cash and pro-
                                                      ceeds including insurance,
                                                      general   intangibles  and
                                                      accounts proceeds
- --------------------------------------------------------------------------------
Boston  Private  Bank & Trust  8-28-98       53144    specific leased equipment
Company
- --------------------------------------------------------------------------------
BankBoston, N.A.               9-2-98        53151*                 Blanket Lien
- --------------------------------------------------------------------------------
BankBoston, N.A.               9-2-98        53152*                 Blanket Lien
- --------------------------------------------------------------------------------
BankBoston, N.A.               9-2-98        53153*                 Blanket Lien
- --------------------------------------------------------------------------------
                           Reagents Applications, Inc.
                          California Secretary of State
- --------------------------------------------------------------------------------
NEC America, Inc.              2-9-96        9604560110          Specific leased
                                                                    equipment
- --------------------------------------------------------------------------------
Safeco Credit Co., Inc.        12-16-97      9735660964          Specific leased
                                                                    equipment
- --------------------------------------------------------------------------------
BostonBank, N.A.               8-31-98       9824460126*            Blanket Lien
- --------------------------------------------------------------------------------
BankBoston, N.A.               9-3-99        9925161008*            Blanket Lien
- --------------------------------------------------------------------------------



- --------
* Filed in connection with the Fleet Credit Line.