PROMISSORY NOTE


$385,645.05                                            Framingham, Massachusetts
                                                                January 11, 2001

         JACK H. KESSLER ("Kessler"), for value received, hereby promises to pay
to the order of SYMBOLLON  CORPORATION,  a Delaware corporation (the "Company"),
the  principal  amount  of  Three  Hundred  Eighty-Five   Thousand  Six  Hundred
Forty-Five Dollars and Five Cents  ($385,645.05),  with interest accruing on the
unpaid  principal  amount  hereof  at the rate of 5.61%  per  annum,  compounded
annually.  All outstanding  principal and interest  accrued thereon shall be due
and payable in full on the earlier to occur of (a) the  termination of Kessler's
employment  with the Company (for any reason) or (b) December 31, 2005.  Kessler
may at any  time  and  from  time  to time  prepay  all or any  portion  of said
principal and interest, without premium or penalty.

         The  holder  of this  Note is  entitled  to the  benefits  of a  Pledge
Agreement  of even date  herewith  by and between  Kessler and the Company  (the
"Pledge  Agreement").  Neither  reference herein to the Pledge Agreement nor any
provision  thereof  shall  affect  or  impair  the  absolute  and  unconditional
obligation of Kessler to pay the principal of and interest, if any, on this Note
as provided herein.  No delay or omission on the part of the holder of this Note
in exercising any right hereunder or under the Pledge Agreement shall operate as
a waiver  of such  right or of any  other  right of such  holder,  nor shall any
delay,  omission  or waiver on any one  occasion be deemed a bar to or waiver of
the same or any other right on any future occasion. All payments of principal of
and  interest,  if any, on this Note shall be payable in  immediately  available
funds at the address of the Company set forth in the Pledge  Agreement.  Kessler
and all endorsers or guarantors of this Note,  regardless of the time,  order or
place of signing,  hereby waive  presentment,  demand,  notice,  protest and all
other  demands  and  notices  in  connection  with  the  delivery,   acceptance,
performance or enforcement of this Note.

         All rights and  obligations  hereunder shall be governed by the laws of
The  Commonwealth  of  Massachusetts  and this Note  shall be deemed to be under
seal.

                                          /s/ Jack H. Kessler
                                          --------------------------------------
                                          Jack H. Kessler

<PAGE>

                                PLEDGE AGREEMENT

         THIS  AGREEMENT,  dated as of the 11th day of January 11, 2001,  by and
between JACK H. KESSLER (the  "Pledgor") and SYMBOLLON  CORPORATION,  a Delaware
corporation (the "Company").

                              W I T N E S S E T H :

         WHEREAS, the Company has agreed to make a loan as of the date hereof in
the principal amount of $385,645.05 to the Pledgor (the "Loan"), such Loan to be
evidenced by the Pledgor's  Promissory Note, payable to the order of the Company
(the "Note"); and

         WHEREAS,  the  obligation of the Company to make the Loan is subject to
the  conditions,  among others,  that the Pledgor shall execute and deliver this
Agreement and grant the security interest hereinafter described;

         NOW,  THEREFORE,  in consideration of the willingness of the Company to
make the Loan to the Pledgor, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, it is hereby agreed as
follows:

         1. Security  Interest.  The Pledgor hereby deposits with and pledges to
the Company 211,281 shares of the Class A Common Stock,  $.001 par value, of the
Company (the "Pledged  Stock"),  and the Pledgor  hereby grants to the Company a
security  interest in the Pledged  Stock as  security  for the due and  punctual
payment and performance of the Secured Obligation described in section 2 hereof.

         2. Secured Obligation.  The security interest hereby granted shall
secure the due and punctual payment of the principal of and interest, if any, on
the Note (the "Secured Obligation").

         3. Special Warranties and Covenants of the Pledgor.  The Pledgor hereby
warrants and covenants to the Company that:

                  (a) The  Pledged  Stock is duly and validly  pledged  with the
         Company in accordance with law and the Pledgor warrants and will defend
         the Company's right,  title and security interest in and to the Pledged
         Stock against the claims and demands of all persons whomsoever.

                  (b) The Pledgor has good title to the Pledged Stock,  free and
         clear of all claims, mortgages,  pledges, liens, security interests and
         other encumbrances of every nature whatsoever.

                  (c) All of the Pledged Stock has been duly and validly  issued
         and is fully paid and nonassessable.

                  (d) The Pledgor will not sell,  convey or otherwise dispose of
         any of the Pledged Stock, nor will the Pledgor create,  incur or permit
         to  exist  any  pledge,  mortgage,  lien,  charge,  encumbrance  or any
         security  interest  whatsoever with respect to any of the Pledged Stock
         or the proceeds thereof,  other than liens on and security interests in
         the Pledged Stock created hereby.

         4.   Distributions.   In  case,  upon  the  dissolution,   winding  up,
liquidation or reorganization of the Company, whether in bankruptcy,  insolvency
or  receivership  proceedings or upon an assignment for the benefit of creditors
or any other  marshalling  of the  assets  and  liabilities  of the  Company  or
otherwise,  any sum shall be paid or any property shall be  distributed  upon or
with  respect to any of the  Pledged  Stock,  such sum shall be paid over to the
Company to be held as collateral  security for the Secured  Obligation.  In case
any stock dividend shall be declared on the Pledged Stock, or any share of stock
or fraction  thereof shall be issued  pursuant to any stock split  involving the
Pledged  Stock,  or  any  distribution  of  capital  (excluding   ordinary  cash
dividends)  shall  be  made on the  Pledged  Stock,  or any  property  shall  be
distributed   upon  or  with   respect  to  the   Pledged   Stock   pursuant  to
recapitalization or  reclassification of the capital of the Company,  the shares
or other property so distributed shall be delivered to the Company to be held as
collateral security for the Secured Obligation.


<PAGE>

         5.       Events of Default.  There shall exist a default under this
Agreement upon the default in the due and punctual payment of any principal of
or interest on the Secured Obligation as and when the same becomes
due and payable (herein called an "Event of Default").

         6. Rights and Remedies of Company.  Upon the  occurrence of an Event of
Default,  such default not having previously been remedied or cured, the Company
shall  have  all  rights  and  remedies  provided  by  law,  including,  without
limitation,  those provided by the Uniform  Commercial  Code, and all rights and
remedies provided in this Agreement and the Note.

         7. Right to  Transfer  into Name of  Company,  etc. In case there shall
exist an  Event  of  Default,  but  subject  to the  provisions  of the  Uniform
Commercial Code or other applicable law, the Company may cause all or any of the
Pledged Stock to be transferred into its name or into the name of its nominee or
nominees.  So long as no Event of Default  shall  exist,  the  Pledgor  shall be
entitled  to  exercise  as the  Pledgor  shall  deem  fit,  but in a manner  not
inconsistent  with the terms  hereof or of the  Secured  Obligation,  the voting
power with respect to the Pledged Stock.

         8. Right of Company to Exercise Voting Power,  etc. In case there shall
exist an Event of Default,  the Company shall be entitled to exercise the voting
power with respect to the Pledged  Stock,  to receive and retain,  as collateral
security  for  the  Secured   Obligation,   any  and  all   dividends  or  other
distributions  at any time  and  from  time to time  declared  or made  upon the
Pledged  Stock,  and to  exercise  any and all  rights of  payment,  conversion,
exchange,  subscription or any other rights, privileges or options pertaining to
the Pledged Stock as if it were the absolute  owner thereof,  including  without
limitation, the right to exchange, at its discretion, any and all of the Pledged
Stock upon the merger, consolidation, reorganization,  recapitalization or other
readjustment  of the Company or, upon the exercise of any such right,  privilege
or option  pertaining  to the Pledged  Stock,  and in connection  therewith,  to
deposit  and  deliver  any and all of the  Pledged  Stock  with  any  committee,
depositary, transfer agent, registrar or other designated agency upon such terms
and conditions as the Company may  determine,  all without  liability  except to
account for property  actually  received,  but the Company shall have no duty to
exercise any of the  aforesaid  rights,  privileges  or options and shall not be
responsible for any failure to do so or delay in so doing.

         9.  Right of  Company  to  Dispose  of  Pledged  Stock,  etc.  Upon the
occurrence  of an Event of  Default,  such  default not having  previously  been
remedied  or  cured,  the  Company  shall  have  the  right at any time or times
thereafter to sell,  resell,  assign and deliver all or any of the Pledged Stock
in one or more parcels at any exchange or broker's board or at public or private
sale.  The Company  will give the Pledgor at least ten (10) days' prior  written
notice at the address of the Pledgor  specified in section 16 hereof of the date
on which and  manner  in which any  private  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 Uniform  Commercial  Code)
that  reasonable  notification  be given of the time and  place of such  sale or
other disposition. Such notice may be given without any demand of performance or
other demand, all such demands being hereby expressly waived by the Pledgor. All
such  sales  shall be at such  commercially  reasonable  price or  prices as the
Company  shall  deem  best.  Upon any such  sale or sales the  Pledged  Stock so
purchased  shall be held by the  purchaser  absolutely  free from any  claims or
rights of whatsoever kind or nature,  including any equity of redemption and any
similar  rights,  all such equity of  redemption  and any similar  rights  being
hereby  expressly  waived and released by the Pledgor.  The proceeds of any such
sale or sales,  together with any other  additional  collateral  security at the
time received and held hereunder,  shall be received and applied:  first, to the
payment of all costs and expenses of such sale, including reasonable  attorneys'
fees;  second,  to the  payment  of the  Secured  Obligation,  and  any  surplus
thereafter  remaining shall be paid to the Pledgor or to whomever may be legally
entitled thereto  (including,  if applicable,  any subordinated  creditor of the
Pledgor).


<PAGE>

         The  Pledgor  recognizes  that the  Company  may be  unable to effect a
public  sale  of  all or a part  of the  Pledged  Stock  by  reason  of  certain
prohibitions  contained in the  Securities  Act of 1933, but may be compelled to
resort to one or more private sales to a restricted group of purchasers, each of
whom will be obligated  to agree,  among other  things,  to acquire such Pledged
Stock  for  its  own  account,  for  investment  and  not  with  a  view  to the
distribution or resale thereof.  The Pledgor  acknowledges that private sales so
made may be at prices and upon other terms less  favorable to the seller than if
such  Pledged  Stock  were sold at public  sales,  and that the  Company  has no
obligation  to delay  sale of any such  Pledged  Stock  for the  period  of time
necessary to permit such Pledged  Stock to be  registered  for public sale under
the Securities Act of 1933. The Pledgor agrees that any such private sales shall
not be deemed to have been made in a  commercially  unreasonable  manner  solely
because they shall have been made under the foregoing circumstances.

         10.  Collection of Amounts  Payable on Account of Pledged  Stock,  etc.
Upon the  occurrence  of any Event of  Default,  the  Company  may,  but without
obligation to do so, demand, sue for and/or collect any money or property at any
time due,  payable or  receivable,  to which it may be  entitled  hereunder,  on
account of or in exchange for any of the Pledged Stock and shall have the right,
for and in the name,  place and stead of the Pledgor,  to execute  endorsements,
assignments  or other  instruments of conveyance or transfer with respect to all
or any of the Pledged Stock.

         11. Care of Pledged Stock in Company's Possession.  Beyond the exercise
of  reasonable  care to assure the safe custody of the Pledged  Stock while held
hereunder,  the Company  shall have no duty or liability to collect any sums due
in respect  thereof or to protect or preserve  rights  pertaining  thereto,  and
shall be relieved of all  responsibility for the Pledged Stock upon surrendering
the same to the Pledgor.

         12.  Waivers,  etc.  The Pledgor  hereby  waives  presentment,  demand,
notice,  protest and, except as is otherwise  provided herein, all other demands
and  notices  in  connection  with  this  Agreement  or the  enforcement  of the
Company's rights  hereunder or in connection with the Secured  Obligation or any
Pledged  Stock;  consents  to and waives  notice of the  granting  of  renewals,
extensions  of time for  payment  or other  indulgences  to the  Company  or the
Pledgor or to any third  party,  or  substitution,  release or  surrender of any
collateral  security  for the  Secured  Obligation,  the  addition or release of
persons  primarily or  secondarily  liable on the Secured  Obligation  or on any
collateral  security  for the  Secured  Obligation,  the  acceptance  of partial
payments on the Secured Obligation or on any collateral security for the Secured
Obligation and/or the settlement or compromise  thereof. No delay or omission on
the part of the Company in  exercising  any right  hereunder  shall operate as a
waiver of such  right or of any other  right  hereunder.  Any waiver of any such
right on any one  occasion  shall not be  construed as a bar to or waiver of any
such right on any future  occasion.  The Pledgor further waives any right he may
have under the  constitution of The  Commonwealth of  Massachusetts or under the
Constitution  of the  United  States  of  America,  to  notice  (other  than any
requirement  of notice  provided  herein) or to a judicial  hearing prior to the
exercise of any right or remedy  provided by this  Agreement  to the Company and
waives his rights,  if any, to set aside or invalidate any sale duly consummated
in accordance  with the foregoing  provisions  hereof on the grounds (if such be
the case) that the sale was consummated  without a prior judicial  hearing.  The
Pledgor's waivers under this section have been made  voluntarily,  intelligently
and  knowingly  and after the Pledgor has been  apprised  and  counseled  by his
attorneys as to the nature thereof and his possible alternative rights.


<PAGE>

         13.  Termination;  Assignment,  etc.  This  Agreement  and the security
interest in the Pledged Stock created  hereby shall  terminate  when the Secured
Obligation  has been  paid and  finally  discharged  in full.  No  waiver by the
Company or by any other holder of the Secured Obligation of any default shall be
effective  unless in writing nor operate as a waiver of any other  default or of
the same default on a future  occasion.  In the event of a sale or assignment by
the Company of all or any of the Secured  Obligation held by it, the Company may
assign or transfer its rights and interest  under this  Agreement in whole or in
part to the  purchaser  or  purchasers  thereof,  whereupon  such  purchaser  or
purchasers  shall become vested with all of the powers and rights of the Company
hereunder,  and the  Company  shall  thereafter  be forever  released  and fully
discharged  from any liability or  responsibility  hereunder with respect to the
rights and interest so assigned.

         14.  Reinstatement.  Notwithstanding the provisions of section 13, this
Agreement  shall continue to be effective or be reinstated,  as the case may be,
if at any time any amount  received  by the  Company  in respect of the  Secured
Obligation is rescinded or must otherwise be restored or returned by the Company
upon the insolvency, bankruptcy,  dissolution,  liquidation or reorganization of
the  Company  or the  Pledgor  or upon  the  appointment  of any  intervenor  or
conservator  of, or trustee or similar  official for, the Company or the Pledgor
or any substantial part of their  respective  properties,  or otherwise,  all as
though such payments had not been made.

         15. Restrictions on Transfer,  etc. To the extent that any restrictions
imposed  by the  charter or by-laws  of the  Company  or any other  document  or
instrument  would in any way affect or impair the  pledge of the  Pledged  Stock
hereunder  or the  exercise  by the  Company  of any  right  granted  hereunder,
including,  without  limitation,  the right of the  Company  to  dispose  of the
Pledged  Stock upon the  occurrence of an Event of Default,  the Pledgor  hereby
waives such  restrictions  and the Pledgor  hereby  agrees that he will take any
further  action  which the  Company  may  reasonably  request  in order that the
Company may obtain and enjoy the full rights and benefits granted to the Company
by this Agreement free of any such restrictions.

         16.      Notices.  Except as otherwise provided herein, all notices to
the Pledgor or to the Company shall be in writing and shall be deemed to have
been sufficiently given or served for all purposes hereof if
personally delivered or mailed by first class mail, postage prepaid, as follows:

                  (a)  if to the Pledgor:

                           Jack H. Kessler
                           c/o Symbollon Corporation
                           37 Loring Drive
                           Framingham, MA  01702
                           Tel:  (508) 620-7676
                           Fax:  (508) 620-7111

                  (b)  if to the Company:

                           Symbollon Corporation
                           37 Loring Drive
                           Framingham, MA  01702
                           Tel:  (508) 620-7676
                           Fax:  (508) 620-7111

or at such other  address as the party to whom such notice is directed  may have
designated  in writing to the other party  hereto.  A notice  shall be deemed to
have been given  upon the  earlier to occur of (i) three (3) days after the date
on which it is deposited in the U.S.  mails or (ii) receipt by the party to whom
such notice is directed.


<PAGE>

         17. Miscellaneous.  This Agreement shall inure to the benefit of and be
binding  upon the Company and the Pledgor and their  respective  successors  and
assigns,  and the term "Company"  shall be deemed to include any other holder or
holders of the Secured Obligation. In case any provision in this Agreement shall
be invalid, illegal or unenforceable,  the validity, legality and enforceability
of the  remaining  provisions  shall  not in any  way be  affected  or  impaired
thereby. This Agreement may be executed in any number of counterparts and by the
different  parties  hereto on separate  counterparts,  each of which shall be an
original, but all of which together shall constitute one instrument.

         18. Governing Law; Jurisdiction;  Waiver of Jury Trial. This Agreement,
including  the  validity  hereof and the rights and  obligations  of the parties
hereunder, shall be construed in accordance with and governed by the laws of The
Commonwealth of Massachusetts.  The Pledgor,  to the extent that he may lawfully
do  so,  hereby  consents  to  service  of  process,  and  to be  sued,  in  The
Commonwealth of Massachusetts  and consents to the jurisdiction of the courts of
The Commonwealth of  Massachusetts  and the United States District Court for the
District of Massachusetts, as well as to the jurisdiction of all courts to which
an appeal may be taken from such courts,  for the purpose of any suit, action or
other proceeding arising out of any of his obligations hereunder or with respect
to the  transactions  contemplated  hereby,  and  expressly  waives  any and all
objections  he may  have as to venue in any such  courts.  The  Pledgor  further
agrees that a summons and complaint commencing an action or proceeding in any of
such courts shall be properly served and shall confer  personal  jurisdiction if
served personally or by certified mail to him at his address provided in section
16  hereof  or as  otherwise  provided  under  the laws of The  Commonwealth  of
Massachusetts.  The Pledgor  irrevocably  waives all right to a trial by jury in
any suit,  action or other  proceeding  instituted  by or against the Pledgor in
respect of his obligations hereunder or the transactions contemplated hereby.

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




                                          By: /s/ Jack H. Kessler
                                             -----------------------------
                                             Jack H. Kessler


                                             SYMBOLLON CORPORATION


                                          By: /s/ Paul C. Desjourdy
                                             ----------------------------
                                             Paul C. Desjourdy, President

<PAGE>

                              SYMBOLLON CORPORATION
                                 37 Loring Drive
                              Framingham, MA 01702

                                                                January 11, 2001
Mr. Jack H. Kessler
c/o Symbollon Corporation
37 Loring Drive
Framingham, MA 01702

Dear Jack:

         Concurrent with the execution of this Letter  Agreement,  you exercised
your stock option to purchase  211,281  shares (the  "Shares") of the  Company's
Class A Common Stock,  $.001 par value per share,  at an exercise  price ranging
from  $1.05 to $3.375 per share,  and you paid for the Shares by  delivering  to
Symbollon Corporation,  a Delaware corporation (the "Company") a Promissory Note
in the  principal  amount of  $385,645.05  (the  "Note"),  secured by the Shares
pursuant to a Pledge  Agreement of even date herewith by and between you and the
Company (the "Pledge Agreement"). Capitalized terms which are not defined herein
shall have the same meanings as ascribed to such terms in the Pledge Agreement.

         You and the Company hereby agree that in the event your employment with
the Company  terminates  prior to December  31, 2005 and the market value of the
Shares on the date of such termination (the "Termination Date") is less than the
principal  and accrued  but unpaid  interest  under the Note at the  Termination
Date,  then,  notwithstanding  anything in the Pledge Agreement to the contrary,
the Shares shall be the Company's sole recourse for payment of the Note. In such
event, you agree to surrender your  certificate for the Shares  accompanied by a
stock  power  executed  in blank to the  Company,  and upon such  surrender  and
delivery of the Shares to the Company,  you shall have no further  obligation to
the  Company  with  respect  to the Note and the Note shall be  returned  to you
marked "Paid In Full."

         This letter  agreement  shall be governed by the  internal  substantive
laws of the Commonwealth of  Massachusetts  and shall be binding upon the heirs,
personal representatives,  executors,  administrators,  successors and permitted
assigns of the parties.  The rights and  obligations  of either party under this
letter  agreement  may only be assigned  with the prior  written  consent of the
other party hereto. This letter agreement  supersedes all prior written and oral
agreements  and  understandings  between the parties and  represents  the entire
agreement  between the parties with respect to the subject matter hereof and may
only be modified  or amended  pursuant  to a written  instrument  signed by both
parties.  The Company is not by reason of this  letter  agreement  obligated  to
continue your employment.

         If the  foregoing  accurately  reflects  our  understanding,  please so
acknowledge by  countersigning  this letter  agreement in the space provided for
your signature below.

                                            Very truly yours,

                                            SYMBOLLON CORPORATION


                                            By: /s/ Paul C. Desjourdy
                                               ------------------------
                                               Paul C. Desjourdy
                                               President and COO

Agreed and Accepted as of this 11th day of January 11, 2000:

/s/ Jack H. Kessler
------------------------
Jack H. Kessler