Exhibit 2.3


                              ASSOCIATED BANC-CORP
                             STOCK OPTION AGREEMENT


                  STOCK  OPTION  AGREEMENT,  dated  as of May 14,  1997,  by and
between Associated Bank-Corp, a Wisconsin corporation (the "Issuer"),  and First
Financial Corporation, a Wisconsin corporation ("Grantee").

                  WHEREAS,  concurrently with the execution and delivery of this
Agreement,  Issuer,  Badger Merger Corp., a Wisconsin  corporation  and a wholly
owned  subsidiary  of Issuer  ("Merger  Sub"),  and Grantee are entering into an
Agreement  and  Plan  of  Merger,  dated  as of the  date  hereof  (the  "Merger
Agreement"),  which provides for, among other things, upon the terms and subject
to the conditions  thereof,  the merger of Merger Sub with and into Grantee (the
"Merger");

                  WHEREAS, as a condition to Grantee's willingness to enter into
the Merger Agreement,  Grantee has requested that the Issuer agree, and in order
to induce Grantee to enter into the Merger  Agreement,  Issuer has so agreed, to
grant to Grantee an option with  respect to certain  shares of  Issuer's  common
stock on the terms and subject to the conditions set forth herein; and

                  WHEREAS, as a condition to Issuer's  willingness to enter into
the Merger Agreement,  the Issuer has requested that Grantee agree, and in order
to induce the Issuer to enter into the Merger Agreement,  Grantee has so agreed,
to grant to Issuer an option with respect to certain shares of Grantee's  common
stock on substantially the same terms as set forth herein;

                  NOW,  THEREFORE,  in consideration of the foregoing and of the
mutual covenants,  representations,  warranties and agreements  contained herein
and in the Merger  Agreement;  and  intending to be legally  bound  hereby,  the
parties agree as follows:

                  1.  Grant  of  Option.   Issuer  hereby   grants   Grantee  an
irrevocable  option (the "Stock Option") to purchase up to (a) 4,465,361  shares
(the "Option Shares") of common stock, $0.01 par value per share, of Issuer (the
"Issuer Common Stock") or (b) if, immediately prior to exercise,  such number of
shares of Issuer  Common Stock is less than 19.9% of the issued and  outstanding
shares of Issuer Common Stock at the time of exercise of the Stock Option,  such
greater  number of shares of Issuer  Common  Stock as equals 19.9% of the issued
and  outstanding  shares of Issuer  Common Stock at such time of exercise of the
Stock Option, in the manner set forth below, at a price of $32.50 per share (the
"Exercise  Price"),  payable  in cash  in  accordance  with  Section  4  hereof.
Capitalized  terms used and not otherwise defined herein shall have the meanings
set forth in the Merger Agreement.

                  2.  Exercise  of  Option.  (a)  Subject to the  provisions  of
Sections 2(c) and (d), the Stock Option may be exercised by Grantee, in whole or
in part, at any time or from time to time following the occurrence of a Purchase
Event (as defined below), provided that, except as provided in the last sentence
of this Section  2(a),  the Stock Option  shall  terminate  and be of no further
force and effect upon the earliest to occur of (i) the Effective  Time,  (ii) 12
months after the first occurrence of





                                        2

a Purchase  Event and (iii)  termination  of the Merger  Agreement in accordance
with its terms prior to the  occurrence of a Purchase  Event  (provided that the
Stock  Option  shall  not  terminate  for a period of 12  months  following  any
occurrence specified in Sections 2(b)(iv)(A) or 2(b)(v)(A); and provided further
that any  purchase of shares upon  exercise of the Stock Option shall be subject
to compliance  with  applicable  law,  including the Bank Holding Company Act of
1956, as amended (the "BHC Act").  Notwithstanding  the termination of the Stock
Option,  Grantee shall be entitled to purchase the Option Shares with respect to
which it has  exercised  the Stock  Option in  accordance  with the terms hereof
prior to the  termination  of the Stock  Option.  The  termination  of the Stock
Option shall not affect any rights  hereunder which by their terms extend beyond
the date of such termination.

                  (b) As  used  herein,  a  "Purchase  Event"  means  any of the
following events:

                  (i) any  person  (other  than  Grantee  or any  subsidiary  of
         Grantee)  shall have  commenced  (as such term is defined in Rule 14d-2
         under the Exchange Act), or shall have filed a  registration  statement
         under the  Securities  Act with  respect to, a tender offer or exchange
         offer to purchase  any shares of Issuer  Common  Stock such that,  upon
         consummation  of such offer,  such person or a "group" (as such term is
         defined under the Exchange Act) of which such person is a member, would
         acquire beneficial  ownership (as such term is defined in Rule 13d-3 of
         the Exchange Act), or the right to acquire beneficial ownership, of 15%
         or more of the then outstanding  Issuer Common Stock (any such offer, a
         "Tender Offer"),  and the Board of Directors shall not have recommended
         against such tender offer or exchange  offer within 10 business days of
         such  commencement or filing or at any time thereafter  shall recommend
         acceptance thereof;

                  (ii) Issuer or any subsidiary of Issuer shall have authorized,
         recommended,  proposed or publicly announced an intention to authorize,
         recommend or propose,  or entered  into,  an agreement  with any person
         (other  than  Grantee or any  subsidiary  of  Grantee)  to (A) effect a
         merger, consolidation or other business combination involving Issuer or
         any of its  subsidiaries  (other than  internal  mergers,  reorganizing
         actions or  consolidations  involving  only  existing  subsidiaries  of
         Issuer),  (B) sell,  lease or otherwise  dispose of assets of Issuer or
         its subsidiaries  aggregating 15% or more of the  consolidated  assets,
         net revenues or net income of Issuer and its subsidiaries or (C) issue,
         sell  or   otherwise   dispose   of   (including   by  way  of  merger,
         consolidation,  share exchange or any similar  transaction)  securities
         representing  15% or more of the  voting  power of Issuer or any of its
         subsidiaries (any of the foregoing, an "Acquisition Transaction");

                   (iii) any person  (other than  Grantee or any  subsidiary  of
         Grantee)  shall have  acquired  beneficial  ownership  (as such term is
         defined in Rule 13d-3 under the  Exchange  Act) or the right to acquire
         beneficial  ownership of, or any "group" (as such term is defined under
         the Exchange Act) shall have been formed which beneficially owns or has
         the right to acquire  beneficial  ownership of, shares of Issuer Common
         Stock (other than trust account shares)  aggregating 15% or more of the
         then outstanding Issuer Common Stock;

                  (iv) (A) the  holders of Issuer  Common  Stock  shall not have
         approved  the  increase  in the number of  authorized  shares of Issuer
         Common Stock or the issuance of Issuer Common Stock in connection  with
         the Merger at the meeting of such  shareholders held for the purpose of
         voting on the  increase  in the number of  authorized  shares of Issuer
         Common





                                        3

         Stock and the issuance of Issuer  Common Stock in  connection  with the
         Merger,  (B) such  meeting  shall not have been held or shall have been
         cancelled prior to termination of the Merger  Agreement or (C) Issuer's
         Board of Directors shall have withdrawn or modified in a manner adverse
         to  Grantee or to  Grantee's  ability to  consummate  the  transactions
         contemplated  by the Merger  Agreement the  recommendation  of Issuer's
         Board of Directors with respect to the Merger  Agreement,  in each case
         after any person  (other  than  Grantee or any  subsidiary  of Grantee)
         shall have (X) publicly announced, or taken actions which have resulted
         in public disclosure of, a proposal, or publicly disclosed an intention
         to make a proposal,  to engage in an Acquisition  Transaction and shall
         not have withdrawn such proposal at least 10 business days prior to the
         stockholders'  meeting  to  consider  the  increase  in the  number  of
         authorized  shares of Issuer  Common  Stock or the  issuance  of Issuer
         Common Stock in connection  with the Merger  (provided  that any public
         disclosures  to the  effect  that such  person  intends  to or may make
         another proposal shall result in the original proposal not being deemed
         to have  been  withdrawn)  or (Y)  filed  an  application  (or  given a
         notice),  whether in draft or final form, to the Federal Reserve Board,
         the OCC, the FDIC or any other governmental or regulatory authority for
         approval to engage in an  Acquisition  Transaction;  provided  that the
         Stock Option shall not be exercisable upon the occurrence  specified in
         Section  2(b)(iv)(A) above unless and until any of the events specified
         in Section 2 (b)(ii) or (iii) above shall have occurred; or

                  (v) (A) there  shall  exist a willful  or  intentional  breach
         under the Merger  Agreement  by Issuer and such  breach  would  entitle
         Grantee to  terminate  the Merger  Agreement;  and (B) within 12 months
         from the date of such  breach,  any of the events  specified in Section
         2(b)(ii) or (iii) above shall have occurred.

As used in this Agreement, "person" shall have the meaning specified in Sections
3(a)(9) and 13(d)(3) of the Exchange Act.

                  (c) In the event Grantee  wishes to exercise the Stock Option,
it shall send to Issuer a written  notice (an "Exercise  Notice" and the date of
which being  herein  referred to as a "Notice  Date")  specifying  (i) the total
number of Option  Shares that it intends to purchase  pursuant to such  exercise
and (ii) a place and date not earlier than three business days nor later than 20
business  days from the Notice Date for the closing of such purchase (a "Closing
Date");  provided  that if any closing of the purchase and sale  pursuant to the
Stock Option (a "Closing")  cannot be  consummated  by reason of any  applicable
order, injunction,  decree, judgment, law or regulation, the period of time that
otherwise would run pursuant to this sentence shall run instead from the date on
which such  restriction  on  consummation  has expired or been  terminated;  and
provided further, without limiting the foregoing,  that if prior notification to
or  approval  of the  Federal  Reserve  Board,  the OCC,  the FDIC or any  other
governmental  or  regulatory  authority  is  required  in  connection  with such
purchase,  Grantee shall promptly file the required  notice or  application  for
approval and shall  expeditiously  process the same (and Issuer shall  cooperate
with Grantee in the filing of any such notice or  application  and the obtaining
of any such approval),  and the period of time that otherwise would run pursuant
to this sentence  shall run instead from the date on which,  as the case may be,
(A) any required  notification period has expired or been terminated or (B) such
approval has been obtained,  and in either event,  any requisite  waiting period
has passed.






                                        4

                  (d)  Notwithstanding  Section  2(c),  in no  event  shall  any
Closing  Date occur later than 18 months after the related  Notice Date,  and if
such Closing shall not have occurred within 18 months after such Notice Date due
to the failure to obtain any required approval of the Federal Reserve Board, the
OCC, the FDIC or any other governmental or regulatory authority, the exercise of
the Stock Option or Substitute  Option  effected on such date shall be deemed to
have expired.  In the event (i) Grantee  receives  official notice that any such
approval  required  for the  purchase  of  Option  Shares  will not be issued or
granted or (ii) a Closing  Date shall not have  occurred  within 18 months after
the related Notice Date due to the failure to obtain any such approval,  Grantee
shall be  entitled  to  exercise  its  rights to  exercise  the Stock  Option in
connection with the resale of Issuer Common Stock or other  securities  pursuant
to a  registration  statement as provided in Section 8. The  provisions  of this
Section 2 and Section 4 shall  apply with  appropriate  adjustments  to any such
exercise.

                  3.  Conditions to Closing.  The  obligation of Issuer to issue
Option  Shares to Grantee  hereunder is subject to the  conditions  that (a) all
consents, approvals, orders or authorizations of, or registrations, declarations
or filings  with,  the Federal  Reserve  Board,  the OCC,  the FDIC or any other
governmental or regulatory  authority,  if any,  required in connection with the
issuance of Option  Shares  hereunder  shall have been  obtained or made, as the
case may be,  and (b) no  order,  injunction  or  decree  issued by any court or
agency of  competent  jurisdiction  or other  legal  restraint  preventing  such
issuance shall be in effect.

                  4. Closing. At any Closing, (a) Issuer will deliver to Grantee
a  certificate  or  certificates  in  definitive   form,  such   certificate  or
certificates to be registered in the name of Grantee, or such other affiliate of
Grantee as Grantee  shall  designate in the  Exercise  Notice and shall bear the
legend  set forth in  Section  11,  representing  the  number  of Option  Shares
designated by Grantee in its Exercise Notice,  which Option Shares shall be free
and clear of all Liens,  and (b) Grantee  will  deliver to Issuer the  aggregate
Exercise Price for the Option Shares so designated  and being  purchased at such
Closing  by wire  transfer  of  immediately  available  funds to a bank  account
designated by Issuer.

                  5. Representations and Warranties of Issuer. Issuer represents
and warrants to Grantee that (a) Issuer is a corporation duly organized, validly
existing and in good  standing  under the laws of the State of Wisconsin and has
full  corporate  power and authority to execute and deliver this  Agreement and,
subject to any  approvals  referred to herein,  to consummate  the  transactions
contemplated hereunder, (b) the execution and delivery of this Agreement and the
consummation of the transactions  contemplated hereby have been duly and validly
approved by the Board of Directors of Issuer and no other corporate  proceedings
on the part of Issuer are necessary to approve this  Agreement and to consummate
the  transactions  contemplated  hereby,  (c) this  Agreement  has been duly and
validly  executed  and  delivered  by Issuer and  (assuming  due  authorization,
execution  and  delivery  by Grantee)  this  Agreement  constitutes  a valid and
binding obligation of Issuer,  enforceable against Issuer in accordance with its
terms,  except as  enforcement  may be limited by general  principles  of equity
whether  applied in a court of law or equity and by  bankruptcy,  insolvency and
similar laws affecting creditors' rights and remedies generally,  (d) Issuer has
taken all necessary  corporate  action to authorize and reserve for issuance and
to permit it to issue, upon exercise of the Stock Option,  and at all times from
the date  hereof  through  the  expiration  of the  Stock  Option  will  have so
reserved,  the  requisite  number of  unissued  shares of  Issuer  Common  Stock
necessary to permit  exercise in full of the Stock  Option,  all of which,  upon
their issuance and delivery in accordance with the terms of this Agreement, will
be validly issued, fully paid and nonassessable





                                        5

(except  as  provided  in  Section  180.0622(2)(b)  of  the  Wisconsin  Business
Corporation  Law),  (e) upon  delivery of such shares of Issuer  Common Stock to
Grantee upon exercise of the Stock  Option,  Grantee will acquire valid title to
all of  such  shares,  free  and  clear  of any  and  all  Liens  of any  nature
whatsoever, (f) the execution and delivery of this Agreement by Issuer does not,
and the  performance  of this  Agreement  by  Issuer  will not (1)  violate  the
certificate of incorporation or by-laws of Issuer,  (2) conflict with or violate
any statute, rule, regulation, order, judgment or decree applicable to Issuer or
by which it or any of its  assets  or  properties  is bound or  affected  or (3)
result in any breach or violation of or  constitute a default (or an event which
with notice or lapse of time or both would become a default) under, or give rise
to any rights of termination,  amendment,  acceleration  or cancellation  of, or
result in the  creation  of any Lien on any of the  property or assets of Issuer
pursuant to, any note, bond, mortgage,  indenture,  contract,  agreement, lease,
license,  or  other  instrument  or  obligation  to which  Issuer  or any of its
subsidiaries is a party or by which Issuer or any of its assets or properties is
bound  or  affected  (except,  in the case of  clauses  (2) and (3)  above,  for
violations,  breaches  or  defaults  which  would  not,  individually  or in the
aggregate,  have a Material  Adverse Effect on Issuer) and (g) any provisions of
the Wisconsin  Business  Corporation Law or Issuer's  Articles of  Incorporation
prohibiting certain business  combinations shall not apply to Grantee in respect
of  Grantee's  acquisition  of some or all of the Option  Shares and (h) Grantee
will not, as a result of its exercise of the Stock Option, become subject to any
anti-takeover provisions, plans or arrangements in place at Issuer.

                  6.   Representations   and  Warranties  of  Grantee.   Grantee
represents  and  warrants  to Issuer  that (a)  Grantee  is a  corporation  duly
organized,  validly existing and in good standing under the laws of the State of
Wisconsin and has full corporate power and authority to execute and deliver this
Agreement and,  subject to any approvals  referred to herein,  to consummate the
transactions  contemplated  hereunder,  (b) the  execution  and delivery of this
Agreement and the consummation of the transactions contemplated hereby have been
duly and  validly  approved  by the Board of  Directors  of Grantee and no other
corporate  proceedings  on the part of Grantee  are  necessary  to approve  this
Agreement and to  consummate  the  transactions  contemplated  hereby,  (c) this
Agreement  has been duly  executed and  delivered by Grantee and  (assuming  due
authorization,  execution and delivery by Issuer) this  Agreement  constitutes a
valid  and  binding  obligation  of  Grantee,  enforceable  against  Grantee  in
accordance  with its  terms,  except as  enforcement  may be  limited by general
principles  of  equity  whether  applied  in a  court  of law or  equity  and by
bankruptcy, insolvency and similar laws affecting creditors' rights and remedies
generally, (d) the execution and delivery of this Agreement by Grantee does not,
and the  performance  of this  Agreement  by Grantee  will not (1)  violate  the
certificate of incorporation or bylaws of Grantee,  (2) conflict with or violate
any statute, rule,  regulation,  order, judgment or decree applicable to Grantee
or by which it or any of its  properties  or assets is bound or  affected or (3)
result in any breach of or  constitute  a default (or an event which with notice
or lapse of time or both  would  become a  default)  under,  or give rise to any
rights of termination,  amendment, acceleration or cancellation of, or result in
the creation of a Lien on any of the property or assets of Grantee  pursuant to,
any note, bond, mortgage,  indenture,  contract,  agreement,  lease, license, or
other  instrument  or obligation to which Grantee is a party or by which Grantee
or any of its properties or assets is bound or affected (except,  in the case of
clauses (2) and (3) above,  for  violations,  breaches,  or defaults which would
not,  individually  or in the  aggregate,  have a  Material  Adverse  Effect  on
Grantee) and (e) any Option  Shares  acquired  upon exercise of the Stock Option
will be, and the Stock Option is being,  acquired by Grantee for its own account
and not with a view to the public  distribution  or resale thereof in any manner
which would be in violation of applicable United States securities laws.





                                        6


                  7.  Adjustment  upon  Changes  in  Capitalization;  Substitute
Option.  (a) In the event of any  change in Issuer  Common  Stock by reason of a
stock dividend, split-up,  recapitalization,  combination, exchange of shares or
similar transaction,  the type and number of shares or securities subject to the
Stock Option, and the Exercise Price therefor,  shall be adjusted appropriately,
and proper provision shall be made in the agreements governing such transaction,
so that Grantee  shall  receive upon exercise of the Stock Option the number and
class of shares or other securities or property that Grantee would have received
in  respect  of Issuer  Common  Stock if the  Stock  Option  had been  exercised
immediately prior to such event or the record date therefor, as applicable.

                  (b) In the event that Issuer shall enter into an agreement (i)
to consolidate  with or merge into any person,  other than Grantee or one of its
subsidiaries,  and shall not be the continuing or surviving  corporation of such
consolidation or merger, (ii) to permit any person, other than Grantee or one of
its  subsidiaries,  to merge into Issuer and Issuer shall be the  continuing  or
surviving corporation, but, in connection with such merger, the shares of Issuer
Common Stock  outstanding  immediately  prior to the consummation of such merger
shall be changed into or exchanged  for stock or other  securities  of Issuer or
any other person or cash or any other  property,  or the shares of Issuer Common
Stock  outstanding  immediately  prior to the  consummation of such merger shall
after such merger represent less than 50% of the outstanding  voting  securities
of  the  merged  company,  or  (iii)  to  sell  or  otherwise  transfer  all  or
substantially all of its assets to any person,  other than Grantee or one of its
subsidiaries,  then,  and in  each  such  case,  the  agreement  governing  such
transaction  shall make proper  provisions so that the Stock Option shall,  upon
the  consummation of any such  transaction and upon the terms and conditions set
forth herein,  be converted  into, or exchanged for, an option (the  "Substitute
Option"),  at the election of Grantee,  of either (A) the Acquiring  Corporation
(as defined  below) or (B) any person that  controls the  Acquiring  Corporation
(any such person being referred to as "Substitute Option Issuer").

                  (c) The  Substitute  Option  shall  have the same terms as the
Stock  Option;  provided that the exercise  price  therefor and number of shares
subject  thereto shall be as set forth in this Section 7; provided  further that
the Substitute Option shall be exercisable immediately upon issuance without the
occurrence of a Purchase  Event;  and provided  further that if the terms of the
Substitute  Option cannot,  for legal  reasons,  be the same as the Stock Option
(subject to the  variations  described in the  foregoing  provisos),  such terms
shall be as similar as possible  and in no event less  advantageous  to Grantee.
Substitute  Option  Issuer  shall also enter into an  agreement  with Grantee in
substantially  the  same  form  as this  Agreement  (subject  to the  variations
described  in  the  foregoing  provisos),  which  shall  be  applicable  to  the
Substitute Option.

                  (d) The Substitute Option shall be exercisable for such number
of shares of  Substitute  Common  Stock  (as  defined  below) as is equal to the
Assigned Value (as defined  below)  multiplied by the number of shares of Issuer
Common Stock for which the Stock Option was theretofore exercisable,  divided by
the Average Price (as defined below), rounded up to the nearest whole share. The
exercise  price per share of Substitute  Common Stock of the  Substitute  Option
(the  "Substitute  Option  Price")  shall  then be equal to the  Exercise  Price
multiplied  by a  fraction  in which the  numerator  is the  number of shares of
Issuer Common Stock for which the Stock Option was  theretofore  exercisable and
the denominator is the number of shares of Substitute Common Stock for which the
Substitute Option is exercisable.






                                        7

                  (e) In no event,  pursuant to any of the foregoing paragraphs,
shall the Substitute  Option be exercisable for more than 19.9% of the aggregate
of the shares of Substitute  Common Stock  outstanding  prior to exercise of the
Substitute  Option. In the event that the Substitute Option would be exercisable
for more than 19.9% of the  aggregate  of the shares of  outstanding  Substitute
Common Stock but for the  limitation in the first sentence of this Section 7(e),
Substitute  Option  Issuer  shall make a cash  payment  to Grantee  equal to the
excess of (i) the value of the  Substitute  Option  without giving effect to the
limitation in the first sentence of this Section 7(e) over (ii) the value of the
Substitute Option after giving effect to the limitation in the first sentence of
this Section 7(e).  This difference in value shall be determined by a nationally
recognized investment banking firm selected by Grantee.

                  (f) Issuer shall not enter into any  transaction  described in
Section 7(b) unless the Acquiring  Corporation  and any person that controls the
Acquiring  Corporation assume in writing all the obligations of Issuer hereunder
and take all other actions that may be necessary so that the  provisions of this
Section 7 are given full force and effect (including,  without  limitation,  any
action that may be  necessary  so that the holders of the other shares of common
stock issued by Substitute Option Issuer are not entitled to exercise any rights
by reason of the issuance or exercise of the Substitute Option and the shares of
Substitute  Common Stock are  otherwise in no way  distinguishable  from or have
lesser  economic  value than other shares of common  stock issued by  Substitute
Option Issuer (other than any  diminution in value  resulting from the fact that
the shares of Substitute Common Stock are restricted  securities,  as defined in
Rule 144 under the Securities Act or any successor provision)).

                  (g)  For  purposes  hereof,   the  following  terms  have  the
following meanings:

                  (1)  "Acquiring  Corporation"  means  (i)  the  continuing  or
         surviving  corporation  of a  consolidation  or merger  with Issuer (if
         other  than  Issuer),  (ii)  Issuer in a merger in which  Issuer is the
         continuing or surviving  corporation and (iii) the transferee of all or
         substantially all of Issuer's assets or deposits.

                  (2)  "Assigned  Value"  means the highest of (A) the price per
         share of  Issuer  Common  Stock at which a Tender  Offer  has been made
         after  the  date   hereof  and  prior  to  the   consummation   of  the
         consolidation,  merger or sale  referred  to in Section  7(b),  (B) the
         price per share to be paid by any third party or the  consideration per
         share to be received by holders of Issuer  Common  Stock,  in each case
         pursuant  to  the   agreement   with   Issuer   with   respect  to  the
         consolidation,  merger or sale  referred  to in Section  7(b),  (C) the
         highest closing sales price per share for Issuer Common Stock quoted on
         the National  Association of Securities  Dealers'  Automated  Quotation
         System (the  "NASDAQS")  (or, if the shares of Issuer  Common Stock are
         not  quoted  thereon,  on the  principal  trading  market on which such
         shares  are  traded as  reported  by a  recognized  source)  during the
         12-month period immediately preceding the consolidation, merger or sale
         referred  to in  Section  7(b)  and (D) in the  event  the  transaction
         referred to in Section  7(b) is a sale of all or  substantially  all of
         Issuer's assets and/or deposits,  an amount equal to (i) the sum of the
         price paid in such sale for such assets and/or deposits and the current
         market value of the  remaining  assets of Issuer,  as  determined  by a
         nationally  recognized  investment  banking  firm  selected by Grantee,
         divided by (ii) the number of shares of Issuer Common Stock outstanding
         at such  time.  In the  event  that a Tender  Offer is made for  Issuer
         Common Stock or an agreement is entered into for a merger





                                        8

         or consolidation  involving consideration other than cash, the value of
         the  securities or other  property  issuable or deliverable in exchange
         for Issuer Common Stock shall be determined by a nationally  recognized
         investment banking firm selected by Grantee.

                  (3) "Average  Price" means the average closing sales price per
         share of a share of Substitute  Common Stock quoted on the NASDAQS (or,
         if the shares of Substitute Common Stock are not quoted thereon, on the
         principal trading market on which such shares are traded as reported by
         a  recognized  source)  for  the one  year  immediately  preceding  the
         consolidation,  merger or sale in question, but in no event higher than
         the closing price of the shares of  Substitute  Common Stock on the day
         preceding  such  consolidation,   merger  or  sale;  provided  that  if
         Substitute Option Issuer is Issuer, the Average Price shall be computed
         with respect to a share of common  stock  issued by Issuer,  the person
         merging into Issuer or by any company which  controls  such person,  as
         Grantee may elect.

                  (4)  "Substitute  Common  Stock"  means the  shares of capital
         stock (or similar equity  interest)  with the greatest  voting power in
         respect of the election of directors (or persons similarly  responsible
         for the direction of the business and affairs) of the Substitute Option
         Issuer.

                  8.  Registration  Rights.  (a) Issuer  shall,  if requested by
Grantee  at any time and from time to time (a) within  three  years of the first
exercise  of  the  Stock  Option  or (b)  for 30  business  days  following  the
occurrence  of either of the events set forth in clauses (i) and (ii) of Section
2(d),  as  expeditiously  as possible  prepare  and file up to two  registration
statements  under the Securities Act if such  registration is necessary in order
to permit the sale or other  disposition of any or all shares of securities that
have been  acquired  by or are  issuable to Grantee  upon  exercise of the Stock
Option in  accordance  with the  intended  method  of sale or other  disposition
stated by Grantee,  including a "shelf'  registration  statement  under Rule 415
under the  Securities Act or any successor  provision,  and Issuer shall use its
best efforts to qualify  such shares or other  securities  under any  applicable
state securities  laws.  Grantee agrees to use its best efforts to cause, and to
cause any  underwriters of any sale or other  disposition to cause,  any sale or
other disposition  pursuant to such  registration  statement to be effected on a
widely  distributed  basis so that upon  consummation  thereof no  purchaser  or
transferee shall own beneficially more than 4.9% of the then outstanding  voting
power of  Issuer.  Issuer  shall use all  reasonable  efforts to cause each such
registration statement to become effective, to obtain all consents or waivers of
other  parties  which  are  required  therefor  and to  keep  such  registration
statement  effective for such period not in excess of 180 days from the day such
registration statement first becomes effective as may be reasonably necessary to
effect such sale or other disposition.  Any registration  statement prepared and
filed under this Section 9, and any sale covered  thereby,  shall be at Issuer's
expense except for underwriting discounts or commissions,  brokers' fees and the
fees and disbursements of Grantee's counsel related thereto.

                  (b) In the  event  that  Grantee  requests  Issuer  to  file a
registration  statement  following the failure to obtain a required approval for
an exercise of the Stock Option as described in Section 2(d), the closing of the
sale or other disposition of Issuer Common Stock or other securities pursuant to
such registration  statement shall occur  substantially  simultaneously with the
exercise of the Stock Option.






                                        9

                  (c) The  obligations  of Issuer under this Section 8 to file a
registration  statement and to maintain its  effectiveness  may be suspended for
one or more periods of time not  exceeding 60 days in the aggregate if the Board
of  Directors  of  Issuer  shall  have   determined  that  the  filing  of  such
registration  statement or the  maintenance of its  effectiveness  would require
premature  disclosure  of  nonpublic   information  that  would  materially  and
adversely affect Issuer.

                  (d) If  during  the  time  periods  referred  to in the  first
sentence of Section 8(a) Issuer effects a registration  under the Securities Act
of Issuer  Common  Stock for its own  account or for any other  stockholders  of
Issuer (other than on Form S-4 or Form S-8, or any successor form), Issuer shall
allow  Grantee  the  right  to  participate  in  such  registration,   and  such
participation   shall  not  affect  the  obligation  of  Issuer  to  effect  two
registration statements for Grantee under this Section 8 ; provided that, if the
managing  underwriters  of such offering  advise Issuer in writing that in their
opinion the number of shares of Issuer Common Stock  requested to be included in
such registration exceeds the number which can be sold in such offering,  Issuer
shall  include the shares  requested to be included  therein by Grantee pro rata
with the shares intended to be included therein by Issuer.

                  (e) Grantee shall provide all information reasonably requested
by Issuer for inclusion in any registration statement to be filed hereunder.  In
connection with any registration  pursuant to this Section 8, Issuer and Grantee
shall  provide each other and any  underwriter  of the offering  with  customary
representations,  warranties,  covenants,  indemnification  and  contribution in
connection with such registration.

                  9. Restrictive Legends.  Each certificate  representing Option
Shares issued to Grantee  hereunder shall initially be endorsed with a legend in
substantially the following form:

                  THE SECURITIES  REPRESENTED BY THIS  CERTIFICATE HAVE NOT BEEN
         REGISTERED  UNDER THE  SECURITIES  ACT OF 1933, AS AMENDED,  AND MAY BE
         REOFFERED OR SOLD ONLY IF SO  REGISTERED  OR IF AN EXEMPTION  FROM SUCH
         REGISTRATION AND APPLICABLE  STATE  SECURITIES LAWS IS AVAILABLE.  SUCH
         SECURITIES ARE ALSO SUBJECT TO ADDITIONAL  RESTRICTIONS  ON TRANSFER AS
         SET FORTH IN THE STOCK OPTION AGREEMENT,  DATED MAY 14, 1997, A COPY OF
         WHICH MAY BE OBTAINED FROM THE ISSUER HEREOF.

                  10.  NASDAQS  Listing.  Upon any exercise of the Stock Option,
Issuer shall use its best efforts to cause the shares of Issuer  Common Stock to
be acquired in connection  with such exercise of the Stock Option to be approved
for  listing on the  NASDAQS  and each other  securities  exchange on which such
shares are listed as soon as practicable after such exercise.

                  11. Assignment;  Third Party  Beneficiaries.  (a) Neither this
Agreement nor any of the rights, interests or obligations of any party hereunder
shall be assigned by any of the parties  hereto  (whether by operation of law or
otherwise)  without  prior  written  consent of the other party;  provided  that
Grantee may assign all or any part of its rights  hereunder to (i) any affiliate
thereof or (ii) any person after the occurrence of a Purchase Event.  Subject to
the  preceding  sentence,  this  Agreement  will be binding  upon,  inure to the
benefit of and be enforceable by the parties and their respective successors and
assigns. This Agreement (including the documents and instruments referred





                                       10

to herein) is not  intended  to confer  upon any person  other than the  parties
hereto any rights or remedies hereunder.

                  (b) Any Option Shares sold by a party in  compliance  with the
provisions of Section 9 shall,  upon  consummation  of such sale, be free of the
restrictions imposed with respect to such shares by this Agreement.  In no event
will any  transferee  of any Option  Shares be entitled to the rights of Grantee
hereunder.

                  (c)  Certificates  representing  shares  sold in a  registered
public  offering  pursuant to Section 8 shall not be required to bear the legend
set forth in Section 9.

                  12.  Enforcement  of the  Agreement.  The parties hereto agree
that  irreparable  damage would occur in the event that any of the provisions of
this  Agreement  were not performed in accordance  with their  specific terms or
were  otherwise  breached.  It is  accordingly  agreed that the parties shall be
entitled to an injunction or injunctions  to prevent  breaches of this Agreement
and to enforce  specifically the terms and provisions hereof in any court of the
United  States or any state having  jurisdiction,  this being in addition to any
other remedy to which they are entitled at law or in equity.

                  13. Entire Agreement.  This Agreement and the Merger Agreement
(together  with the other  documents and  instruments  referred to in the Merger
Agreement)  constitute the entire  agreement and supersede all prior  agreements
and understandings, both written and oral, among the parties with respect to the
subject matter hereof.

                  14.  Further  Assurances.  Each party will execute and deliver
all such further  documents and  instruments and take all such further action as
may be necessary in order to consummate the transactions contemplated hereby.

                  15.  Severability.  Any term or  provision  of this  Agreement
which  is  invalid  or  unenforceable  in any  jurisdiction  shall,  as to  that
jurisdiction,   be   ineffective   to  the   extent   of  such   invalidity   or
unenforceability  without rendering invalid or unenforceable the remaining terms
and provisions of this Agreement or affecting the validity or  enforceability of
any of the terms or provisions of this Agreement in any other  jurisdiction.  If
any  provision  of  this  Agreement  is so  broad  as to be  unenforceable,  the
provision shall be interpreted to be only so broad as is enforceable.

                  16. Notices.  All notices and other  communications  hereunder
shall be in writing and shall be deemed given if delivered personally, mailed by
registered or certified mail (return receipt  requested) or delivered by express
courier (with  confirmation) to the parties at the following  addresses (or such
other address for a party as shall be specified by like notice):

                  (a)       if to Grantee, to:

                                 First Financial Corporation
                                 1305 Main Street
                                 Stevens Point, Wisconsin  54481
                                 Attention:  Robert M. Salinger, General Counsel






                                       11

                           With a copy to:

                                 Hogan & Hartson, L.L.P.
                                 555 13th Street, N.W.
                                 Washington, D.C.  20004
                                 Attention:  Stuart G. Stein

                  and

                  (b)      if to Issuer, to:

                                 Associated Banc-Corp
                                 112 North Adams Street
                                 Green Bay, Wisconsin  54307
                                 Attention:  Brian R. Bodager, General Counsel

                           With a copy to:

                                 Shearman & Sterling
                                 599 Lexington Avenue
                                 New York, New York  10022
                        Attention: Creighton O'M. Condon

                  17.  Governing  Law. This  Agreement  shall be governed by and
construed in accordance with the laws of the State of Wisconsin,  without regard
to any applicable conflicts of law.

                  18. Headings. The headings contained in this Agreement are for
reference  purposes  only  and  shall  not  affect  in any  way the  meaning  or
interpretation of this Agreement.

                  19.   Counterparts.   This   Agreement   may  be  executed  in
counterparts,  all of which shall be considered and shall become  effective when
counterparts  have been signed by each of the parties and delivered to the other
parties,   it  being  understood  that  all  parties  need  not  sign  the  same
counterpart.

                  20. Expenses. Except as otherwise expressly provided herein or
in the Merger Agreement, all costs and expenses incurred in connection with this
Agreement and the  transactions  contemplated  hereby shall be paid by the party
incurring such expense.

                  21. Amendments;  Waiver.  This Agreement may be amended by the
parties  hereto and the terms and  conditions  hereof  may be waived  only by an
instrument in writing signed on behalf of each of the parties hereto, or, in the
case of a waiver,  by an  instrument  signed  on  behalf  of the  party  waiving
compliance.






                                       12

                  IN  WITNESS  WHEREOF,  Issuer and  Grantee  have  caused  this
Agreement to be executed by their respective  officers thereunto duly authorized
as of the date first above written.

                                            ASSOCIATED BANC-CORP



                                            By: /s/ H.B. Conlon
                                               ----------------------------
                                               Name:  H.B. Conlon
                                               Title: Chief Executive Officer


                                            FIRST FINANCIAL CORPORATION


                                            By: /s/ John C. Seramur
                                                ------------------------
                                                Name: John C. Seramur
                                                Title: Chief Executive Officer