DEBENTURE EXCHANGE AND REGISTRATION RIGHTS AGREEMENT

DEBENTURE EXCHANGE AND REGISTRATION RIGHTS AGREEMENT, dated as of January 13,
1997, by and among Aon Capital A, a Delaware business trust (the "Trust"), Aon
Corporation,  a Delaware corporation ("Aon"), and Morgan Stanley & Co.
Incorporated  and Goldman, Sachs & Co. (collectively, the "Purchasers") of the
8.205% Capital Securities of the Trust.

     1.   Certain Definitions. For purposes of this Debenture Exchange and
Registration Rights Agreement, the following terms shall have the following
respective meanings:

     (a)  "Capital Securities Exchange and Registration Rights Agreement" means
the Capital Securities Exchange and Registration Rights Agreement in respect of
the Capital Securities dated as of January 13, 1997 among Aon, the Trust and the
Purchasers.

     (b)  "Commission" means the Securities and Exchange Commission, or any
other federal agency at the time administering the Exchange Act or the
Securities Act, whichever is the relevant statute for the particular purpose.

     (c)  "Debentures" means the 8.205% Junior Subordinated Deferrable Interest
Debentures due January 1, 2027 of Aon, to be issued pursuant to the Indenture.

     (d)  "Effective Time", in the case of (i) an Exchange Offer, means the date
on which the Commission declares the Exchange Offer registration statement
effective or on which such registration statement otherwise becomes effective
and (ii) a Shelf Registration, means the date on which the Commission declares
the Shelf Registration effective or on which the Shelf Registration otherwise
becomes effective.

     (e)  "Exchange Act" means the Securities Exchange Act of 1934, or any
successor thereto, as amended from time to time.

     (f)  "Exchange Debentures" has the meaning set forth in Section 2(a)
hereof.

     (g)  "Exchange Guarantee" has the meaning set forth in Section 2(a) hereof.

     (h)  "Exchange Offer" has the meaning set forth in Section 2(a) hereof.

     (i)  "Exchange Registration" has the meaning set forth in Section 3(c)
hereof.

     (j)  "Exchange Securities" has the meaning set forth in Section 2(a)
hereof.

     (k)  "Guarantee" means the Guarantee of Aon with respect to the Securities,
to the extent set forth in the Guarantee Agreement.

     (l)  "Guarantee Agreement" means the Capital Securities Guarantee Agreement
dated as of January 13, 1997 between Aon and The Bank of New York, a New York

 
banking corporation, as Guarantee Trustee (together with its successors and
assigns "Guarantee Trustee") for the benefit of the holders of the Securities.

     (m)  "Guarantee Exchange and Registration Rights Agreement" means the
Guarantee Exchange and Registration Rights Agreement in respect of the Guarantee
dated as of January 13 , 1997 among Aon, the Trust and the Purchasers.

     (n)  The term "holder" has the meaning set forth in the Capital Securities
Exchange and Registration Rights Agreement; provided, however, that if all the
Registrable Securities and all the Securities cease to be outstanding, then it
shall have the meaning set forth in the Indenture with respect to the
Debentures.

     (o)  "Indemnified Person" has the meaning set forth in Section 6(a) hereof.

     (p)  "Indenture" means the Indenture dated as of January 13, 1997 between
Aon and The Bank of New York, as Debenture Trustee, as supplemented by the First
Supplemental Indenture dated as of January 13, 1997, and as further amended or
supplemented from time to time.

     (q)  "Issue Date" means January 13, 1997.

     (r)  "Liquidation Amount" means the stated liquidation preference of the
Securities.

     (s)  "New Guarantee Agreement" has the meaning set forth in the Guarantee
Exchange and Registration Rights Agreement.

     (t)  The term "person" means any individual, corporation, estate,
partnership, joint venture, association, joint stock company, limited liability
company, trust, unincorporated association or government or any agency or
political subdivision thereof, or any other entity of whatever nature.

     (u)  "Purchase Agreement" means the Purchase Agreement dated January 8,
1997 among Aon, the Trust and the Purchasers.

     (v)  "Registrable Securities" has the meaning set forth in the Capital
Securities Exchange and Registration Rights Agreement; provided, however, that
if all the Registrable Securities and all the Securities cease to be
outstanding, then it shall mean the Debentures which have not been sold,
directly or indirectly, pursuant to an effective registration statement under
the Securities Act.

     (w)  "Registration Default" has the meaning set forth in Section 2(c)
hereof.

     (x)  "Registration Expenses" has the meaning set forth in Section 4 hereof.

     (y)  "Resale Period" has the meaning set forth in the Capital Securities
Exchange and Registration Rights Agreement.

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     (z)  "Securities" means, collectively, the $800,000,000 aggregate
Liquidation Amount of the 8.205% Capital Securities, Liquidation Amount $1,000
per Capital Security, of the Trust to be issued and sold to the Purchasers, and
any securities issued in exchange therefor or in lieu thereof pursuant to the
Trust Agreement; provided, however, that if all the Registrable Securities and
all the Securities cease to be outstanding, then it shall mean the Debentures
which have been registered under the Securities Act.

     (aa) "Securities Act" means the Securities Act of 1933, or any successor
thereto, as amended from time to time.

     (bb) "Shelf Registration" has the meaning set forth in Section 2(b) hereof.

     (cc) "Special Interest" has the meaning set forth in Section 2(c) hereof.

     (dd) "Trust Agreement" means the Amended and Restated Trust Agreement dated
as of January 13, 1997 among Aon, as Depositor, The Bank of New York, as
Property Trustee, The Bank of New York (Delaware), as Delaware Trustee, the
Administrative Trustees named therein and the holders, from time to time, of
undivided beneficial interests in the assets of the Trust.

     (ee) "Trust Indenture Act" means the Trust Indenture Act of 1939, or any
successor thereto, and the rules, regulations and forms promulgated thereunder,
as amended from time to time.

     Unless the context otherwise requires, any reference herein to a "Section"
or "clause" refers to a Section or clause, as the case may be, of this Debenture
Exchange and Registration Rights Agreement, and the words "herein," "hereof" and
"hereunder" and other words of similar import refer to this Debenture Exchange
and Registration Rights Agreement as a whole and not to any particular Section
or other subdivision.

     2.   Registration Under the Securities Act.

     (a)  If Aon and the Trust file a registration statement pursuant to Section
2(a) of the Capital Securities Exchange and Registration Rights Agreement, then
Aon and the Trust agree, jointly and severally, to include in such registration
statement an offer to exchange (the "Exchange Offer") all of the Debentures for
a like aggregate principal amount of a new series of junior subordinated
deferrable interest debentures of Aon which are substantially identical to the
Debentures (and which are entitled to the benefits of the Indenture which will
be qualified under the Trust Indenture Act) except that they have been
registered pursuant to an effective registration statement under the Securities
Act and such new debentures will not contain provisions for Special Interest or
provisions restricting transfer in the absence of registration under the
Securities Act (such new debentures hereinafter called "Exchange Debentures").
Such registration statement shall also relate to, and the consummation of the
Exchange Offer shall be conditioned upon the consummation of, an offer to
exchange the Securities for substantially identical capital securities of the
Trust pursuant to the Capital Securities Exchange and Registration Rights
Agreement (the "Exchange Securities") and to an offer to exchange the Guarantee
for a substantially identical guarantee of Aon pursuant to

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the Guarantee Exchange and Registration Rights Agreement (the "Exchange
Guarantee").  Aon and the Trust agree, jointly and severally, to use their
reasonable best efforts to cause such registration statement to become effective
under the Securities Act within 180 days of the Issue Date.  The Exchange Offer
will be registered under the Securities Act on the appropriate form.  The
Exchange Offer shall be deemed to have been completed upon the completion of the
exchange of the Exchange Debentures for all the Debentures pursuant to the
Exchange Offer.

     (b)  If (i) Aon and the Trust file a "shelf" registration statement
pursuant to Section 2(b) of the Capital Securities Exchange and Registration
Rights Agreement without also filing a registration statement pursuant to
Section 2(a) thereof or (ii) none of the Securities or the Registrable
Securities is outstanding and the Exchange Offer has not been effected, then in
the case of clause (i), such "shelf" registration statement shall provide for
the registration of the Debentures and, in the case of clause (ii) none of the
Securities or the Registrable Securities is outstanding and the Exchange Offer
has not been effected, Aon shall file under the Securities Act, as soon as
practicable, a "shelf" registration statement providing for the registration of,
and the sale on a continuous or delayed basis by the holders of, all of the
Registrable Securities, pursuant to Rule 415 under the Securities Act and/or any
similar rule that may be adopted by the Commission (in each case, the "Shelf
Registration"). In the case of clause (i) only, the Shelf Registration shall
also provide for the registration of the Securities pursuant to the Capital
Securities Exchange and Registration Rights Agreement and for the registration
of the Guarantee pursuant to the Guarantee Exchange and Registration Rights
Agreement. Aon and, if applicable, the Trust agree, jointly and severally, to
use their reasonable best efforts to cause the Shelf Registration to become or
be declared effective and to keep such Shelf Registration continuously effective
for a period ending on the earlier of (A) the third anniversary of the Issue
Date or (B) such time as there are no longer any Registrable Securities
outstanding. Aon and, if applicable, the Trust further agree, jointly and
severally, to supplement or make amendments to the Shelf Registration, as and
when required by the rules, regulations or instructions applicable to the
registration form used by Aon and, if applicable, the Trust for such Shelf
Registration or by the Securities Act or rules and regulations thereunder for
shelf registration, and Aon and, if applicable, the Trust agree, jointly and
severally, to furnish to the holders of the Registrable Securities copies of any
such supplement or amendment prior to its being used and/or filed with the
Commission.

     (c)  In the event that (i) Aon and, if applicable, the Trust have not filed
the registration statement relating to the Exchange Offer (or, if applicable,
the Shelf Registration) on or before the 150th day after the Issue Date, or (ii)
such registration statement (or, if applicable, the Shelf Registration) has not
become effective or been declared effective by the Commission on or before the
180th day after the Issue Date, or (iii) any of the Exchange Offer, the exchange
offers contemplated by the Capital Securities Exchange and Registration Rights
Agreement and the exchange offer contemplated by the Guarantee Exchange and
Registration Rights Agreement has not been completed within 210 days after the
Issue Date (if the Exchange Offer is then required to be made) or (iv) any
registration statement required by Section 2(a) or 2(b) is filed and declared
effective but shall thereafter cease to be effective for five business days
(except as specifically permitted herein) without being succeeded by an
additional registration statement filed and declared

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effective (each such event referred to in clauses (i) through (iv), a
"Registration Default"), then interest will accumulate (in addition to the
stated interest rate on the Debentures) at the rate of 0.25% per annum on the
principal amount of the Debentures for the period from the occurrence of the
Registration Default until such time as no Registration Default is in effect.
Such additional interest (the "Special Interest") will be payable in cash semi-
annually in arrears on each July 1 and January 1 in accordance with, and subject
to the deferral provisions of, the Indenture. Special Interest, if any, will be
computed on the basis of a 365 or 366 day year, as the case may be, and the
number of days actually elapsed.

     (d)  Any reference herein to a registration statement shall be deemed to
include any document incorporated therein by reference as of the applicable
Effective Time and any reference herein to any post-effective amendment to a
registration statement shall be deemed to include any document incorporated
therein by reference as of a time after such Effective Time.

     3.   Registration Procedures.

     If Aon and, if applicable, the Trust file a registration statement pursuant
to Section 2(a) or Section 2(b), the following provisions shall apply:

     (a)  At or before the Effective Time of the Exchange Offer or the Shelf
Registration, as the case may be, Aon shall qualify the Indenture, the New
Guarantee Agreement, if applicable, and the Trust Agreement, if applicable,
under the Trust Indenture Act.

     (b)  In the event that such qualification would require the appointment of
a new trustee under any of the Indenture, the New Guarantee Agreement or the
Trust Agreement, such new trustee shall be appointed thereunder pursuant to the
applicable provisions thereof.

     (c)  In connection with the joint and several obligations of Aon and the
Trust with respect to the registration of the Exchange Securities, the Exchange
Guarantee and the Exchange Debentures, as contemplated by Section 2(a) (the
"Exchange Registration"), if applicable, Aon and the Trust shall, as soon as
reasonably possible (or as otherwise specified):

               (i)   prepare and file with the Commission, as soon as
          practicable but no later than 150 days after the Issue Date, a
          registration statement with respect to the Exchange Registration on
          any form which may be utilized by Aon and the Trust and which shall
          permit the Exchange Offer and resales of Exchange Securities by 
          broker-dealers during the Resale Period to be effected as contemplated
          by Section 2(a) hereof, and use its reasonable best efforts to cause
          such registration statement to become effective as soon as practicable
          thereafter;

               (ii)  as soon as practicable prepare and file with the Commission
          such amendments and supplements to such registration statement and the
          prospectus included therein as may be necessary to effect and maintain
          the effectiveness of such registration statement for the periods and
          purposes

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          contemplated in Section 2(a) hereof and as may be required by the
          applicable rules and regulations of the Commission and the
          instructions applicable to the form of such registration statement,
          and promptly provide each broker-dealer holding Exchange Securities
          with such number of copies of the prospectus included therein (as then
          amended or supplemented), in conformity in all material respects with
          the requirements of the Securities Act and the Trust Indenture Act and
          the rules and regulations of the Commission promulgated thereunder, as
          such broker-dealer reasonably may request prior to the expiration of
          the Resale Period, for use in connection with resales of Exchange
          Securities;

               (iii)  promptly notify each broker-dealer that has requested or
          received copies of the prospectus included in such registration
          statement, and confirm such advice in writing, (A) when such
          registration statement or the prospectus included therein or any
          prospectus amendment or supplement or post-effective amendment has
          been filed, and, with respect to such registration statement or any
          post-effective amendment, when the same has become effective, (B) of
          the receipt of any comments by the Commission and by the Blue Sky or
          securities commissioner or regulator of any state with respect thereto
          or any request by the Commission for amendments or supplements to such
          registration statement or prospectus or for additional information,
          (C) of the issuance by the Commission of any stop order suspending the
          effectiveness of such registration statement or the initiation or
          threatening by the Commission of any proceedings for that purpose, (D)
          if at any time the joint and several representations and warranties of
          Aon and the Trust contemplated by Section 5 cease to be true and
          correct in all material respects, (E) of the receipt by either Aon or
          the Trust of any notification with respect to the suspension of the
          qualification of the Exchange Securities and the Exchange Guarantee
          for sale in any United States jurisdiction or the initiation or, to
          Aon's or the Trust's knowledge, threatening of any proceeding for such
          purpose, or (F) at any time during the Resale Period when a prospectus
          is required to be delivered under the Securities Act, that such
          registration statement, prospectus, prospectus amendment or supplement
          or post-effective amendment does not conform in all material respects
          to the applicable requirements of the Securities Act and the Trust
          Indenture Act and the rules and regulations of the Commission
          promulgated thereunder or contains an untrue statement of a material
          fact or omits to state a material fact required to be stated therein
          or necessary to make the statements therein not misleading in light of
          the circumstances then existing;

               (iv)   in the event that Aon and the Trust would be required,
          pursuant to Section 3(c)(iii)(F) above, to notify any broker-dealers
          holding Exchange Securities, without delay prepare and furnish to each
          such holder a reasonable number of copies of a prospectus supplemented
          or amended so that, as thereafter delivered to purchasers of such
          Exchange Securities during the Resale Period, such prospectus shall
          conform in all material

                                       6

 
          respects to the applicable requirements of the Securities Act and the
          Trust Indenture Act and the rules and regulations of the Commission
          promulgated thereunder and shall not contain an untrue statement of a
          material fact or omit to state a material fact required to be stated
          therein or necessary to make the statements therein not misleading in
          light of the circumstances then existing;

               (v)     use their reasonable best efforts to obtain the
          withdrawal of any order suspending the effectiveness of such
          registration statement or any post-effective amendment thereto at the
          earliest practicable date;

               (vi)    use their reasonable best efforts to (A) register or
          qualify the Exchange Securities and the Exchange Guarantee under the
          securities laws or blue sky laws of such jurisdictions as are
          contemplated by Section 2(a) no later than the commencement of the
          Exchange Offer, (B) keep such registrations or qualifications in
          effect and comply with such laws so as to permit the continuance of
          offers, sales and dealings therein in such jurisdictions until the
          expiration of the Resale Period and (C) take any and all other actions
          as may be reasonably necessary or advisable to enable each broker-
          dealer holding Exchange Securities to consummate the disposition
          thereof in such jurisdictions; provided, however, that neither Aon nor
          the Trust shall be required for any such purpose to (1) qualify to do
          business in any jurisdiction wherein it would not otherwise be
          required to qualify but for the requirements of this Section 3(c)(vi),
          (2) consent to general service of process in any such jurisdiction or
          (3) in the case of Aon, make any changes to its charter or by-laws or
          any agreement between it and its stockholders or in the case of the
          Trust, make any changes to the Trust Agreement;

               (vii)   use their reasonable best efforts to obtain the consent
          or approval of each United States governmental agency or authority,
          whether federal, state or local, which may be required to effect the
          Exchange Registration, the Exchange Offer and the offering and sale of
          Exchange Securities by broker-dealers during the Resale Period;

               (viii)  provide a CUSIP number for all Exchange Securities, not
          later than the applicable Effective Time; and

               (ix)    comply with all applicable rules and regulations of the
          Commission, and make generally available to all holders of Securities
          as soon as practicable but no later than eighteen months after the
          Effective Time, an earnings statement of Aon and its subsidiaries
          complying with Section 11 (a) of the Securities Act (including, at the
          option of Aon, Rule 158 thereunder).

     (d)  In connection with the joint and several obligations of Aon and the
Trust with respect to the Shelf Registration, if applicable, Aon and, if
applicable, the Trust shall use

                                       7

 
their reasonable best efforts to cause the Shelf Registration to become
effective to permit the sale of the Registrable Securities by the holders
thereof in accordance with the intended method or methods of distribution
thereof described in the Shelf Registration. In connection therewith, Aon and,
if applicable, the Trust shall as soon as reasonably possible (or as otherwise
specified):

               (i)     prepare and file with the Commission, as soon as
          practicable, a registration statement with respect to the Shelf
          Registration on any form which may be utilized by Aon and, if
          applicable, the Trust and which shall permit the disposition of the
          Registrable Securities in accordance with the intended method or
          methods thereof, as specified in writing to Aon and, if applicable,
          the Trust by the holders of the Registrable Securities and use their
          reasonable best efforts to cause such registration statement to become
          effective as soon as practicable thereafter;

               (ii)    as soon as practicable, prepare and file with the
          Commission such amendments and supplements to such registration
          statement and the prospectus included therein as may be necessary to
          effect and maintain the effectiveness of such registration statement
          for the period specified in Section 2(b) hereof and as may be required
          by the applicable rules and regulations of the Commission and the
          instructions applicable to the form of such registration statement and
          furnish to the holders of the Registrable Securities copies of any
          such supplement or amendment simultaneously with or prior to its being
          used or filed with the Commission;

               (iii)   comply with the provisions of the Securities Act
          applicable to Aon or, if applicable, the Trust in connection with the
          disposition of all of the Registrable Securities covered by such
          registration statement in accordance with the intended methods of
          disposition by the holders thereof, set forth in such registration
          statement;

               (iv)    provide (A) the holders of the Registrable Securities to
          be included in such registration statement and not more than one
          counsel for all the holders of such Registrable Securities, (B) the
          underwriters (which term, for purposes of this Debenture Exchange and
          Registration Rights Agreement, shall include a person deemed to be an
          underwriter within the meaning of Section 2(11) of the Securities
          Act), if any, thereof, (C) the sales or placement agent, if any,
          therefor and (D) one counsel for such underwriters or agents, if any,
          reasonable opportunity to participate in the preparation of such
          registration statement, each prospectus included therein or filed with
          the Commission, and each amendment or supplement thereto;

               (v)     for a reasonable period prior to the filing of such
          registration statement, and throughout the period specified in Section
          2(b), make available at reasonable times at Aon's principal place of
          business or such other reasonable place for inspection by the persons
          referred to in Section 3(d)(iv) who shall certify to Aon and, if
          applicable, the Trust that they have

                                       8

 
          a current intention to sell the Registrable Securities pursuant to the
          Shelf Registration such financial and other information and books and
          records of Aon and, if applicable, the Trust, and cause the officers,
          employees, counsel and independent certified public accountants of Aon
          and, if applicable, the Trust to respond to such inquiries, as shall
          be reasonably necessary, in the judgment of the respective counsel
          referred to in such Section, to conduct a reasonable investigation
          within the meaning of Section 11 of the Securities Act; provided,
          however, that each such party shall be required to maintain in
          confidence and not to disclose to any other person any information or
          records reasonably designated by Aon as being confidential, until such
          time as (A) such information becomes a matter of public record
          (whether by virtue of its inclusion in such registration statement or
          otherwise, except by disclosure by such party in breach of this
          Agreement), or (B) such person shall be required so to disclose such
          information pursuant to the subpoena or order of any court or other
          governmental agency or body having jurisdiction over the matter
          (subject to, and only to the extent required by, the requirements of
          such order, and only after such person shall have given Aon prompt
          prior written notice of such requirement);

               (vi)    promptly notify the selling holders of Registrable
          Securities, the sales or placement agent, if any, therefor and the
          managing underwriter or underwriters, if any, thereof and confirm such
          advice in writing, (A) when such registration statement or the
          prospectus included therein or any prospectus amendment or supplement
          or post-effective amendment has been filed, and, with respect to such
          registration statement or any post-effective amendment, when the same
          has become effective, (B) of any comments by the Commission and by the
          Blue Sky or securities commissioner or regulator of any state with
          respect thereto or any request by the Commission for amendments or
          supplements to such registration statement or prospectus or for
          additional information, (C) of the issuance by the Commission of any
          stop order suspending the effectiveness of such registration statement
          or the initiation or threatening by the Commission of any proceedings
          for that purpose, (D) if at any time the joint and several
          representations and warranties of Aon and, if applicable, the Trust
          contemplated by Section 3(d)(xv)(A) or Section 5 cease to be true and
          correct in all material respects, (E) of the receipt by either Aon or
          the Trust of any notification with respect to the suspension of the
          qualification of the Registrable Securities and, if applicable, the
          Guarantee, for sale in any jurisdiction or the initiation or, to Aon's
          or the Trust's knowledge, threatening of any proceeding for such
          purpose, or (F) at any time when a prospectus is required to be
          delivered under the Securities Act, that such registration statement,
          prospectus, prospectus amendment or supplement or post-effective
          amendment, or any document incorporated by reference in any of the
          foregoing, does not conform in all material respects to the applicable
          requirements of the Securities Act and the Trust Indenture Act and the
          rules and regulations of the Commission promulgated thereunder or
          contains an untrue statement of a material fact or omits to state any
          material

                                       9

 
          fact required to be stated therein or necessary to make the statements
          therein not misleading in light of the circumstances then existing;

               (vii)   use their best efforts to obtain the withdrawal of any
          order suspending the effectiveness of such registration statement or
          any post-effective amendment thereto at the earliest practicable date;

               (viii)  if requested by any managing underwriter or underwriters,
          any placement or sales agent or any holder or counsel for the holders
          of Registrable Securities, promptly incorporate in a prospectus
          supplement or post-effective amendment such information as is required
          by the applicable rules and regulations of the Commission and as such
          managing underwriter or underwriters, such agent or such holder
          specifies should be included therein relating to the terms of the sale
          of such Registrable Securities, including, without limitation,
          information with respect to the Liquidation Amount or the principal
          amount, as the case may be, of Registrable Securities being sold by
          any holder or agent or to any underwriters, the name and description
          of such holder, agent or underwriter, the offering price of such
          Registrable Securities and any discount, commission or other
          compensation payable in respect thereof, the purchase price being paid
          therefor by such underwriters and with respect to any other terms of
          the offering of the Registrable Securities, to be sold by such holder
          or agent or to such underwriters; and make all required filings of
          such prospectus supplement or post-effective amendment promptly after
          notification of the matters to be incorporated in such prospectus
          supplement or post-effective amendment;

               (ix)    furnish to each holder of Registrable Securities, each
          placement or sales agent, if any, therefor, each underwriter, if any,
          thereof and the respective counsel referred to in Section 3(d)(iv) an
          executed copy of such registration statement, each such amendment and
          supplement thereto (in each case including all exhibits thereto and
          documents incorporated by reference therein) and such number of copies
          of such registration statement (excluding exhibits thereto and
          documents incorporated by reference therein unless specifically so
          requested by such holder, agent or underwriter, as the case may be)
          and of the prospectus included in such registration statement
          (including each preliminary prospectus and any summary prospectus), in
          conformity with the requirements of the Securities Act and the Trust
          Indenture Act and the rules and regulations of the Commission
          promulgated thereunder, and such other documents, as such holder,
          agent, if any, and underwriter, if any, may reasonably request in
          order to facilitate the offering and disposition of the Registrable
          Securities owned by such holder, offered or sold by such agent or
          underwritten by such underwriter and to permit such holder, agent and
          underwriter to satisfy the prospectus delivery requirements of the
          Securities Act; and each of Aon and, if applicable, the Trust hereby
          consents to the use of such prospectus (including such preliminary and
          summary

                                       10

 
          prospectus) and any amendment or supplement thereto by each such
          holder and by any such agent and underwriter, in each case in the form
          most recently provided to such party by Aon and the Trust, in
          connection with the offering and sale of the Registrable Securities
          covered by the prospectus (including such preliminary and summary
          prospectus) or any supplement or amendment thereto;

               (x)     use their reasonable best efforts to (A) register or
          qualify the Registrable Securities to be included in such registration
          statement and, if applicable, the Guarantee under such securities laws
          or blue sky laws of such jurisdictions as any holder of such
          Registrable Securities and each placement or sales agent, if any,
          therefor and underwriter, if any, thereof shall reasonably request,
          (B) keep such registrations or qualifications in effect and comply
          with such laws so as to permit the continuance of offers, sales and
          dealings therein in such jurisdictions during the period the Shelf
          Registration is required to remain effective under Section 2(b) above
          and for so long as may be necessary to enable any such holder, agent
          or underwriter to complete its distribution of Securities pursuant to
          such registration statement and (C) take any and all other actions as
          may be reasonably necessary or advisable to enable each such holder,
          agent, if any, and underwriter, if any, to consummate the disposition
          in such jurisdictions of Registrable Securities; provided, however,
          that neither Aon nor, if applicable, the Trust shall be required for
          any such purpose to (1) qualify to do business in any jurisdiction
          wherein it would not otherwise be required to qualify but for the
          requirements of this Section 3(d)(x), (2) consent to general service
          of process in any such jurisdiction, (3) in the case of Aon, make any
          changes to its charter or by-laws or any agreement between it and its
          shareholders or, if applicable, in the case of the Trust, make any
          changes to the Trust Agreement;

               (xi)    use their reasonable best efforts to obtain the consent
          or approval of each governmental agency or authority, whether federal,
          state or local, which may be required to effect the Shelf Registration
          or the offering or sale in connection therewith or to enable the
          selling holder or holders to offer, or to consummate the disposition
          of, their Registrable Securities;

               (xii)   cooperate with the holders of the Registrable Securities
          and the managing underwriters, if any, to facilitate the timely
          preparation and delivery of certificates representing Registrable
          Securities to be sold, which certificates shall be printed,
          lithographed or engraved, or produced by any combination of such
          methods, and which shall not bear any restrictive legends; and, in the
          case of an underwritten offering, enable such Registrable Securities
          to be in such denominations and registered in such names as the
          managing underwriters may request at least two business days prior to
          any sale of the Registrable Securities;

                                       11

 
               (xiii)  provide a CUSIP number for all Registrable Securities,
          not later than the applicable Effective Time;

               (xiv)   enter into not more than one underwriting agreement,
          engagement letter, agency agreement, "best efforts" underwriting
          agreement or similar agreement, as appropriate, including (without
          limitation) provisions relating to indemnification and contribution
          substantially the same as those set forth in Section 6 hereof, and
          take such other actions in connection therewith as any holders of
          Registrable Securities aggregating at least 25% in aggregate
          Liquidation Amount, or in aggregate principal amount, as the case may
          be, of the Registrable Securities at the time outstanding shall
          reasonably request in order to expedite or facilitate the disposition
          of such Registrable Securities; provided, that Aon and, if applicable,
          the Trust shall not be required to (i) enter into any such agreement
          more than once with respect to all of the Registrable Securities and
          may delay entering into such agreement until the consummation of any
          underwritten public offering which Aon and, if applicable, the Trust
          shall have then undertaken or (ii) enter into any engagement letter,
          agency agreement, "best effort" underwriting agreement or similar
          agreements whatsoever with respect to the Registrable Securities, and
          provided further, that Aon and, if applicable, the Trust shall not be
          obligated to enter into any such agreement with a broker-dealer which
          results in the need for a "qualified independent underwriter" (within
          the meaning of the Rules of Fair Practice and the By-Laws of the
          National Association of Securities Dealers, Inc. ("NASD") or any
          successor thereto, as amended from time to time (the "Rules and By-
          Laws of NASD"));

               (xv)    whether or not an agreement of the type referred to in
          Section (3)(d)(xiv) hereof is entered into and whether or not any
          portion of the offering contemplated by such registration statement is
          an underwritten offering or is made through a placement or sales agent
          or any other entity, (A) make such representations and warranties to
          the holders of such Registrable Securities and the placement or sales
          agent, if any, therefor and the underwriters, if any, thereof
          substantially the same as those set forth in Section 1 of the Purchase
          Agreement and such other representations and warranties as are
          customarily made with respect to the offering of debt securities
          pursuant to any appropriate agreement or to a registration statement
          on the applicable form under the Securities Act; (B) obtain an opinion
          or opinions of counsel to Aon and, if applicable, the Trust
          substantially the same as the opinions provided for in Section 5 of
          the Purchase Agreement with such additions, substitutions or deletions
          of such matters as are customarily covered in opinions for an
          underwritten offering, addressed to such holder or holders and the
          placement or sales agent, if any, therefor and the underwriters, if
          any, thereof and dated the effective date of such registration
          statement (and if such registration statement contemplates an
          underwritten offering of a part or all of the Registrable Securities,
          dated the date of the closing under the underwriting agreement
          relating thereto) (it

                                       12

 
          being agreed that the matters to be covered by such opinion shall also
          include, without limitation, the absence of governmental approvals
          required to be obtained in connection with the Shelf Registration, the
          offering and sale of the Registrable Securities, this Debenture
          Exchange and Registration Rights Agreement or any agreement of the
          type referred to in Section (3)(d)(xiv) hereof, except such approvals
          as may be required under state securities or blue sky laws; and the
          compliance in all material respects as to form of such registration
          statement and any documents incorporated by reference therein and of
          the Indenture, the Guarantee Agreement, if applicable, and the Trust
          Agreement, if applicable, with the requirements of the Securities Act
          and the Trust Indenture Act and the rules and regulations of the
          Commission promulgated thereunder, respectively); and, such opinion
          shall also state that such counsel has no reason to believe that, as
          of the date of the opinion and of the registration statement or most
          recent post-effective amendment thereto, as the case may be, such
          registration statement and the prospectus included therein, as then
          amended or supplemented, and the documents incorporated by reference
          therein (in each case other than the financial statements and other
          financial information contained therein) contains or contained an
          untrue statement of a material fact or omits or omitted to state
          therein a material fact necessary to make the statements therein not
          misleading (in the case of such documents, in the light of the
          circumstances existing at the time that such documents were filed with
          the Commission under the Exchange Act); (C) obtain a "cold comfort"
          letter or letters from the independent certified public accountants of
          Aon and, if applicable, the Trust addressed to the selling holders of
          Registrable Securities, the placement or sales agent, if any, therefor
          and the underwriters, if any, thereof, dated (i) the effective date of
          such registration statement and (ii) the effective date of any
          prospectus supplement to the prospectus included in such registration
          statement or post-effective amendment to such registration statement;
          (D) deliver such other documents and certificates, including officers'
          certificates, as may be reasonably requested by any holders of at
          least 25% in aggregate Liquidation Amount, or in aggregate principal
          amount, as the case may be, of the Registrable Securities at the time
          outstanding or the placement or sales agent, if any, therefor and the
          managing underwriters, if any, thereof to evidence the accuracy of the
          representations and warranties made pursuant to clause (A) above or
          those contained in Section 5(a) hereof and the compliance with or
          satisfaction of any agreements or conditions contained in the
          underwriting agreement or other agreement entered into by Aon and, if
          applicable, the Trust; and (E) undertake such obligations relating to
          expense reimbursement, indemnification and contribution as are
          provided in Section 6 hereof;

               (xvi)   notify in writing each holder of Registrable Securities
          of any proposal by Aon and the Trust to amend or waive any provision
          of this Debenture Exchange and Registration Rights Agreement pursuant
          to Section 9(h) hereof and of any amendment or waiver effected
          pursuant

                                       13

 
          thereto, each of which notices shall contain the text of the amendment
          or waiver proposed or effected, as the case may be;

               (xvii)  in the event that any broker-dealer registered under the
          Exchange Act shall underwrite any Registrable Securities or
          participate as a member of an underwriting syndicate or selling group
          or "assist in the distribution" (within the meaning of the Rules and
          By-Laws of NASD) thereof, whether as a holder of such Registrable
          Securities or as an underwriter, a placement or sales agent or a
          broker or dealer in respect thereof, or otherwise, assist such broker-
          dealer in complying with the requirements of such Rules and By-Laws,
          including, without limitation, by (A) if such Rules or By-Laws,
          including Schedule E thereto (or any successor thereto), shall so
          require, engaging a "qualified independent underwriter" (as defined in
          such Schedule (or any successor thereto)) to participate in the
          preparation of the registration statement relating to such Registrable
          Securities, to exercise usual standards of due diligence in respect
          thereto and, if any portion of the offering contemplated by such
          registration statement is an underwritten offering or is made through
          a placement or sales agent, to recommend the yield of such Registrable
          Securities, (B) indemnifying any such qualified independent
          underwriter to the extent of the indemnification of underwriters
          provided in Section 6 hereof (or to such other customary extent as may
          be required by such underwriter), and (C) providing such information
          to such broker-dealer as may be required in order for such broker-
          dealer to comply with the requirements of the Rules and By-Laws of
          NASD; and

               (xviii)  comply with all applicable rules and regulations of the
          Commission, and make generally available to its holders of the
          Securities as soon as practicable but in any event not later than
          eighteen months after the effective date of such registration
          statement, an earnings statement of Aon and its subsidiaries complying
          with Section 11(a) of the Securities Act (including, at the option of
          Aon, Rule 158 thereunder).

     (e) In the event that Aon and, if applicable, the Trust would be required,
pursuant to Section 3(d)(vi)(F) above, to notify the selling holders of
Registrable Securities, the placement or sales agent, if any, therefor and the
managing underwriters, if any, thereof, Aon and, if applicable, the Trust shall
without delay prepare and furnish to each such holder, to each placement or
sales agent, if any, and to each underwriter, if any, a reasonable number of
copies of a prospectus supplemented or amended so that, as thereafter delivered
to purchasers of Registrable Securities, such prospectus shall conform in all
material respects to the applicable requirements of the Securities Act and the
Trust Indenture Act and the rules and regulations of the Commission promulgated
thereunder and shall not contain an untrue statement of a material fact or omit
to state a material fact required to be stated therein or necessary to make the
statements therein not misleading in light of the circumstances then existing.
Each broker-dealer holding Exchange Securities and each holder of Registrable
Securities agrees that upon receipt of any notice from Aon and, if applicable,
the Trust pursuant to Section 3(c)(iii)(F) or 3(d)(vi)(F) hereof, as the case
may be, such holder shall

                                       14

 
forthwith discontinue the disposition of Exchange Securities or Registrable
Securities, as the case may be, pursuant to the registration statement
applicable to such Exchange Securities or Registrable Securities, as the case
may be, until such holder shall have received copies of such amended or
supplemented prospectus, and if so directed by Aon and, if applicable, the
Trust, such holder shall deliver to Aon (at Aon's expense) all copies, other
than permanent file copies, then in such holder's possession of the prospectus
covering such Exchange Securities or Registrable Securities, as the case may be,
at the time of receipt of such notice.

     (f) Aon and, if applicable, the Trust may require each holder of
Registrable Securities as to which any registration is being effected to furnish
in writing to Aon and, if applicable, the Trust such information regarding such
holder and such holder's intended method of distribution of such Registrable
Securities as Aon and the Trust may from time to time reasonably request in
writing, but only to the extent that such information is required in order to
comply with the Securities Act. Each such holder agrees to notify Aon and, if
applicable, the Trust as promptly as practicable of any inaccuracy or change in
information previously furnished by such holder to Aon and, if applicable, the
Trust or of the occurrence of any event in either case as a result of which any
prospectus relating to such registration contains or would contain an untrue
statement of a material fact regarding such holder or such holder's intended
method of distribution of such Registrable Securities or omits to state any
material fact regarding such holder or such holder's intended method of
distribution of such Registrable Securities required to be stated therein or
necessary to make the statements therein not misleading in light of the
circumstances then existing, and promptly to furnish to Aon and, if applicable,
the Trust any additional information required to correct and update any
previously furnished information or required so that such prospectus shall not
contain, with respect to such holder or the distribution of such Registrable
Securities, an untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary to make the statements therein
not misleading in light of the circumstances then existing. Each such holder
shall comply with the provisions of the Securities Act applicable to such holder
with respect to the disposition by such holder of Registrable Securities covered
by such registration statement in accordance with the intended methods of
disposition by such holder set forth in such registration statement.

     (g) Until the expiration three years after the Issue Date, Aon will not,
and will not permit any of its "affiliates" (as defined in Rule 144 under the
Securities Act) to, resell any of the Securities which constitute "restricted
securities" under Rule 144 that have been reacquired by any of them except
pursuant to an effective registration statement under the Securities Act or any
exemption therefrom; provided, however, that, for purposes of this paragraph,
"affiliates" shall not include the Purchasers or any of their affiliates other
than Aon and its subsidiaries, officers, managers and directors.

     4. Registration Expenses.

     If Aon and, if applicable, the Trust file a registration statement pursuant
to Section 2(a) or Section 2(b), the following provisions shall apply:

     Aon agrees to bear and to pay or cause to be paid promptly upon request
being made therefor all expenses incident to the performance by Aon and, if
applicable, the Trust

                                       15

 
or compliance with this Debenture Exchange and Registration Rights Agreement,
including, without limitation, (a) all Commission and any NASD registration and
filing fees and expenses, (b) all fees and expenses in connection with the
qualification of the Securities and, if applicable, the Guarantee for offering
and sale under the state securities and blue sky laws referred to in Section
3(d)(x) hereof, including reasonable fees and disbursements of counsel in
connection with such qualifications, (c) all expenses relating to the
preparation, printing, distribution and reproduction of each registration
statement required to be filed hereunder, each prospectus included therein or
prepared for distribution pursuant hereto, each amendment or supplement to the
foregoing, and the certificates representing the Securities and all documents
relating hereto, (d) messenger and delivery expenses, (e) fees and expenses of
the Debenture Trustee under the Indenture, the Issuer Trustees under the Trust
Agreement and, if applicable, the Guarantee Trustee under the Guarantee
Agreement, if applicable, and of any escrow agent or custodian, (f) internal
expenses (including, without limitation, all salaries and expenses of Aon's
officers and employees performing legal or accounting duties), (g) fees,
disbursements and expenses of counsel and independent certified public
accountants of Aon and, if applicable, the Trust (including the expenses of any
opinions or "cold comfort" letters required by or incident to such performance
and compliance), (h) fees, disbursements and expenses of any "qualified
independent underwriter" engaged pursuant to Section 3(d)(xvii) hereof, (i)
fees, disbursements and expenses of one counsel for the holders of Registrable
Securities retained in connection with a Shelf Registration, as selected by the
holders of at least a majority in aggregate Liquidation Amount, or the aggregate
principal amount, as the case may be, of the Registrable Securities being
registered, and fees, expenses and disbursements of any other persons, including
special experts, retained by Aon or, if applicable, the Trust in connection with
such registration (collectively, the "Registration Expenses"). To the extent
that any Registration Expenses are incurred, assumed or paid by any holder of
Registrable Securities or any placement or sales agent therefor or underwriter
thereof, Aon shall reimburse such person for the full amount of the Registration
Expenses so incurred, assumed or paid promptly after receipt of a written
request therefor. Notwithstanding the foregoing, the holders of the Registrable
Securities being registered shall pay all agency or brokerage fees and
commissions and underwriting discounts and commissions attributable to the sale
of such Registrable Securities and the fees and disbursements of any counsel or
other advisors or experts retained by such holders (severally or jointly), other
than the counsel and experts specifically referred to above, transfer taxes on
resale of any of the Securities by such holders and any advertising or
solicitation expenses other than expenses specifically referred to above
incurred by or on behalf of such holders in connection with any offers they may
make.

     5. Representations and Warranties.

     Aon and, if applicable, the Trust, jointly and severally, represent and
warrant to, and agree with, each Purchaser and each of the holders from time to
time of Registrable Securities that:

     (a) Each registration statement covering Registrable Securities, the
Guarantee, if applicable, and the Debentures and each prospectus (including any
preliminary or summary prospectus) contained therein or furnished pursuant to
Section 3(d)(ix) hereof and any

                                       16

 
further amendments or supplements to any such registration statement or
prospectus, when it becomes effective or is filed with the Commission, as the
case may be, and, in the case of an underwritten offering of Registrable
Securities, at the time of the closing under the underwriting agreement relating
thereto, will conform in all material respects to the applicable requirements of
the Securities Act and the Trust Indenture Act, the rules and regulations of the
Commission promulgated thereunder and any such registration statement and any
amendment thereto will not contain an untrue statement of a material fact or
omit to state a material fact required to be stated therein or necessary to make
the statements therein not misleading and any such prospectus or any amendment
or supplement thereto will not contain an untrue statement of a material fact or
omit to state a material fact required to be stated therein or necessary to make
the statements therein not misleading in light of the circumstances then
existing; and at all times subsequent to the Effective Time of any such
registration statement when a prospectus would be required to be delivered under
the Securities Act, other than from (i) such time as a notice has been given to
holders of Registrable Securities pursuant to Section 3(c)(iii)(F) or Section
3(d)(vi)(F) hereof until (ii) such time as Aon and, if applicable, the Trust
furnish an amended or supplemented prospectus pursuant to Section 3(c)(iv) or
Section 3(e) hereof, as the case may be, each such registration statement, and
each prospectus (including any summary prospectus) contained therein or
furnished pursuant to Section 3(c) or Section 3(d)(ix) hereof, as then amended
or supplemented, will conform in all material respects to the applicable
requirements of the Securities Act and the Trust Indenture Act and the rules and
regulations of the Commission promulgated thereunder and will not contain an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading in
the light of the circumstances then existing; provided, however, that this
representation and warranty shall not apply to any statements or omissions made
in reliance upon and in conformity with information furnished in writing to Aon
and, if applicable, the Trust by a holder of Registrable Securities or any
placement or sales agent therefor or underwriter thereof expressly for use
therein.

     (b) Any documents incorporated by reference in any prospectus referred to
in Section 5(a) hereof, when they become or became effective or are or were
filed with the Commission, as the case may be, will conform or conformed in all
material respects to the requirements of the Securities Act or the Exchange Act,
as applicable, and none of such documents will contain or contained an untrue
statement of a material fact or will omit or omitted to state a material fact
required to be stated therein or necessary to make the statements therein not
misleading; provided, however, that this representation and warranty shall not
apply to any statements or omissions made in reliance upon and in conformity
with information furnished in writing to Aon and the Trust, if applicable, by a
holder of Registrable Securities expressly for use therein.

     (c) The representations and warranties of the Trust, if applicable, and Aon
contained in Section 1 of the Purchase Agreement are true and correct with the
same force and effect as though expressly made at and as of the date hereof.

     6. Indemnification.

                                       17

 
     (a) Upon the registration of the Registrable Securities pursuant to Section
2 hereof, and in consideration of the agreements of the Purchasers contained
herein, and as an inducement to the Purchasers to purchase the Securities, the
Trust and Aon, jointly and severally, agree to indemnify and hold harmless each
of the holders of Registrable Securities to be included in such registration,
and each person who participates as a placement or sales agent or as an
underwriter in any offering or sale of such Registrable Securities and each
person, if any, who controls such holder, or such placement or sales agent, if
any, or such underwriter, if any, within the meaning of Section 15 of the Act or
Section 20 of the Exchange Act (each an "Indemnified Person") as follows:

               (i) against any and all losses, claims, damages and liabilities
          (including, without limitation, any legal or other expenses reasonably
          incurred in connection with defending or investigating any such action
          or claim) caused by any untrue statement or alleged untrue statement
          of a material fact contained in any registration statement under which
          such Registrable Securities were registered under the Securities Act,
          or caused by any omission or alleged omission to state therein a
          material fact required to be stated therein or necessary to make the
          statements therein not misleading or caused by any untrue statement or
          alleged untrue statement of a material fact contained in any
          preliminary, final or summary prospectus (or any amendment or
          supplement thereto) contained in such registration statement or caused
          by any omission or alleged omission to state therein of a material
          fact necessary in order to make the statements therein, in the light
          of the circumstances under which they were made, not misleading,
          except insofar as such losses, claims, damages or liabilities are
          caused by any such untrue statement or omission that was made in
          reliance upon and in conformity with written information relating to
          such Indemnified Person furnished to the Trust and Aon by, or on
          behalf of, such Indemnified Person expressly for use in such
          registration statement or such preliminary, final or summary
          prospectus (or any amendment or supplement thereto);

               (ii) against any and all losses, claims, damages and liabilities
          whatsoever to the extent of the aggregate amount paid in settlement of
          any litigation, or investigation or proceeding by any governmental
          agency or body, commenced or threatened, or of any claim whatsoever
          based upon any such untrue statement or omission, or any such alleged
          untrue statement or omission (except as made in reliance upon and in
          conformity with information relating to such Indemnified Person
          furnished by, or on behalf of, such Indemnified Person as aforesaid),
          if such settlement is effected with the written consent of the Trust
          and Aon; and

               (iii) against any and all expense whatsoever (including the fees
          and disbursements of counsel chosen by such Indemnified Person),
          reasonably incurred in investigating, preparing or defending against
          any litigation, or investigation or proceeding by any governmental
          agency or body, commenced or threatened, or any claim whatsoever based
          upon any such untrue statement or omission, or any such alleged untrue
          statement or

                                       18

 
          omission (except as made in reliance upon and in conformity with
          information relating to such Indemnified Person furnished by, or on
          behalf of, such Indemnified Person as aforesaid) to the extent that
          any such expense is not paid under (i) or (ii) above.

provided, however, that indemnification with respect to any prospectus shall not
inure to the benefit of any holder of Registrable Securities or Exchange
Securities from whom the Person asserting any loss, claim, damage, liability or
expense purchased such Securities, if a copy of the prospectus (as then amended
or supplemented and furnished by Aon to such holder) was not sent or given by or
on behalf of such person or to such person if such is required by law at or
prior to the sale of such Registrable Securities or Exchange Securities, as the
case may be, and if the prospectus (as so amended and supplemented) would have
cured the defect giving rise to such loss, claim, damage, liability or expense.

     (b) Aon may require, as a condition to including any Registrable Securities
in any registration statement filed pursuant to Section 2 hereof and to entering
into any placement or underwriting agreement with respect thereto, that Aon
shall have received an undertaking reasonably satisfactory to them from the
holder of such Registrable Securities and from each placement agent or
underwriter named in any such placement agreement or underwriting agreement,
severally and not jointly, to indemnify and hold harmless the Trust and Aon and
each person, if any, who controls the Trust or Aon within the meaning of Section
15 of the Securities Act or Section 20 of the Exchange Act against any and all
loss, claim, damage, liability and expense described in the indemnity contained
in subsection (a) of this Section, but only with respect to untrue statements or
omissions, or alleged untrue statements or omissions, made in any registration
statement under which such Registrable Securities were registered under the
Securities Act, or any preliminary, final or summary prospectus contained
therein as furnished by the Trust or Aon to any such holder, agent or
underwriter (or any amendment or supplement thereto), in reliance upon and in
conformity with written information relating to such holder, or such placement
or sales agent, if any, or such underwriter, if any, furnished to the Trust and
Aon by or on behalf of such holder, or such placement or sales agent, if any, or
such underwriter, if any, expressly for use in such registration statement or
such preliminary, final or summary prospectus (or any amendment or supplement
thereto).

     (c) Each indemnified party shall give prompt notice to each indemnifying
party of any action commenced against it in respect of which indemnity may be
sought hereunder but failure to so notify an indemnifying party shall not
relieve it from any liability which it may have otherwise than on account of
this indemnity agreement. An indemnifying party may participate at its own
expense in the defense of such action. In no event shall the indemnifying
parties be liable for the fees and expenses of more than one counsel (in
addition to any local counsel) for all indemnified parties in connection with
any one action or separate but similar or related actions in the same
jurisdiction arising out of the same general allegations or circumstances;
provided, however, that when more than one of such holders, such placement or
sales agents, if any, or such underwriters, if any, is an indemnified party each
such holder, placement or sales agent or such underwriter, as the case may be,
shall be entitled to separate counsel (in addition to any local counsel) in each
such jurisdiction to the extent such holder, placement or sales agent or such
underwriter, as the case may be, may

                                       19

 
have interests conflicting with those of the other holder, placement or sales
agent or such underwriter, as the case may be.  No indemnifying party shall,
without the prior written consent of the indemnified party, effect any
settlement of any pending or threatened proceeding in respect of which any
indemnified party is or could have been a party and indemnity could have been
sought hereunder by such indemnified party, unless such settlement includes an
unconditional release of such indemnified party from all liability on claims
that are the subject matter of such proceeding.

     In order to provide for just and equitable contribution in circumstances in
which the indemnity agreement provided for in this Section 6 is for any reason
held to be unavailable to such holders, such placement or sales agents, if any,
or such underwriters, if any, in accordance with its terms, the Trust, Aon and
such holders, such placement and sales agents, if any, and such underwriters, if
any,  shall contribute to the aggregate losses, liabilities, claims, damages and
expenses of the nature contemplated by said indemnity agreement incurred by the
Trust, Aon and such holders, such placement and sales agents, if any, and such
underwriters, if any, in such proportions as is appropriate to reflect the
relative benefits received by the Trust and Aon on the one hand and such
holders, such placement and sales agents, if any, and such underwriters, if any,
on the other.  The relative benefits received by the Trust and Aon on the one
hand and such holders, such placement and sales agents, if any, and such
underwriters, if any, on the other shall be deemed to be in such proportion
represented by the percentage that the total commissions and underwriting
discounts received by such holders, such placement and sales agents, if any, and
such underwriters, if any, to the date of such liability bears to the total
sales price (before deducting expenses) received by the Trust and such holders,
such placement and sales agents, if any, and such underwriters, if any, from the
sale of such Securities made to the date of such liability, and the Trust and
Aon are jointly and severally responsible for the balance.  If, however, the
allocation provided by the immediately preceding sentence is not permitted by
applicable law or if such holders, such placement and sales agents, if any, and
such underwriters, if any, failed to give the notice required under this
subsection (c), then the Trust, Aon and such holders, such placement and sales
agents, if any, and such underwriters, if any, shall contribute to such
aggregate losses, liabilities, claims, damages and expenses in such proportion
as is appropriate to reflect not only such relative benefits but also the
relative fault of the Trust and Aon on the one hand and such holders, such
placement and sales agents, if any, and such underwriters, if any, on the other
in connection with the statements or omissions which resulted in such
liabilities, claims, damages and expenses, as well as any other relevant
equitable considerations.  The relative fault shall be determined by reference
to, among other things, whether the untrue or alleged untrue statement of a
material fact or the omission or alleged omission to state a material fact
relates to information supplied by the Trust and Aon on the one hand or is
supplied by, or on behalf of, such holders, such placement or sales agents, if
any, and such underwriters, if any, on the other and the parties' relative
intent, knowledge, access to information and opportunity to correct or prevent
such statement or omission.  The Trust, Aon and such holders, such placement or
sales agents, if any, and such underwriters, if any, agree that it would not be
just and equitable if contributions pursuant to this paragraph were determined
pro rata (even if such holders, such placement or sales agents, if any, and such
underwriters, if any, were treated as one entity for such purpose) or by any
other method of allocation which does not take account of the equitable
considerations referred to in this paragraph.  Notwithstanding the provisions of

                                       20

 
this paragraph, such holders, such placement or sales agents, if any, and such
underwriters, if any, shall not be required to contribute any amount in excess
of the amount by which the total price at which the Securities referred to in
the second sentence of this paragraph that were offered and sold to the public
through such holders, such placement or sales agents, if any, and such
underwriters, if any, exceeds the amount of any damages that such holders, such
placement or sales agents, if any, and such underwriters, if any, have otherwise
been required to pay by reason of such untrue or alleged untrue statement or
omission or alleged omission. No person guilty of fraudulent misrepresentation
(within the meaning of Section 11(f) of the Securities Act) shall be entitled
under this paragraph to contribution from any person who was not guilty of such
fraudulent misrepresentation. For purposes of this Section, each person, if any,
who controls any such holders, such placement or sales agents, if any, and such
underwriters, if any, within the meaning of Section 15 of the Securities Act or
Section 20 of the Exchange Act shall have the same rights to contribution as
such holders, such placement or sales agents, if any, and such underwriters, if
any, and each person, if any, who controls the Trust or Aon within the meaning
of Section 15 of the Securities Act or Section 20 of the Exchange Act shall have
the same rights to contribution as the Trust or Aon.

     7.Underwritten Offerings.

     (a) Selection of Underwriters. If any of the Registrable Securities covered
by the Shelf Registration are to be sold pursuant to an underwritten offering,
the managing underwriter or underwriters thereof shall be designated by the
holders of at least a majority in aggregate Liquidation Amount, or aggregate
principal amount, as the case may be, of the Registrable Securities to be
included in such offering, provided that such designated managing underwriter or
underwriters is or are reasonably acceptable to the Trust, if applicable, and
Aon.

     (b) Participation by Holders. Each holder of Registrable Securities hereby
agrees with each other such holder that no such holder may participate in any
underwritten offering hereunder unless such holder (i) agrees to sell such
holder's Registrable Securities on the basis provided in any underwriting
arrangements approved by the persons entitled hereunder to approve such
arrangements and (ii) completes and executes all questionnaires, powers of
attorney, indemnities, underwriting agreements and other documents reasonably
required under the terms of such underwriting arrangements.

     (c) Consolidated Earnings Statements. In the event of an underwritten
offering, Aon agrees to make generally available to holders of Securities as
soon as practicable, but in any event not later than eighteen months after the
effective date of the applicable registration statement (as defined in Rule
158(c) under the Securities Act), a consolidated earnings statement of Aon
(which need not be audited) complying with Section 11 (a) of the Securities Act
and the rules and regulations of the Commission thereunder (including, at the
option of Aon, Rule 158 under the Securities Act)

                                       21

 
     8. Rule 144.

     Aon covenants to the holders of Registrable Securities that to the extent
it shall be required to do so under the Exchange Act, Aon shall timely file the
reports required to be filed by it under the Exchange Act or the Securities Act
(including, but not limited to, the reports under Sections 13 and 15(d) of the
Exchange Act referred to in subparagraph (c)(1) of Rule 144 adopted by the
Commission under the Securities Act) and the rules and regulations adopted by
the Commission thereunder, and shall take such further action as any holder of
Registrable Securities may reasonably request, all to the extent required from
time to time to make Rule 144 available to such holder for the sale of
Registrable Securities without registration under the Securities Act within the
limitations of the exemption provided by Rule 144 under the Securities Act, as
such Rule may be amended from time to time, or any similar or successor rule or
regulation hereafter adopted by the Commission. Upon the request of any holder
of Registrable Securities in connection with that holder's sale pursuant to Rule
144, Aon shall deliver to such holder a written statement as to whether it has
complied with such requirements.

     9. Miscellaneous.

     (a) No Inconsistent Agreements. Each of the Trust and Aon represents,
warrants, covenants and agrees that it has not granted, and shall not grant,
registration rights with respect to Registrable Securities or any other
securities which would be inconsistent with the terms contained in this
Debenture Exchange and Registration Rights Agreement and that the Capital
Securities Exchange and Registration Rights Agreement and the Guarantee Exchange
and Registration Rights Agreement should be construed to be consistent with the
terms hereof.

     (b) Specific Performance. The parties hereto acknowledge that there would
be no adequate remedy at law if any party fails to perform any of its
obligations hereunder and that each party may be irreparably harmed by any such
failure and accordingly agree that each party, in addition to any other remedy
to which it may be entitled at law or in equity, shall be entitled to compel
specific performance of the obligations of any other party under this Debenture
Exchange and Registration Rights Agreement in accordance with the terms and
conditions of this Debenture Exchange and Registration Rights Agreement, in any
court of the United States or any State thereof having jurisdiction.

     (c) Notices. All notices, requests, claims, demands, waivers and other
communications hereunder shall be in writing and shall be deemed to have been
duly given when delivered by hand, if delivered personally or by courier, or
three days after being deposited in the mail (registered or certified mail,
postage prepaid, return receipt requested) as follows:  if to the Trust or to
Aon, then to Aon Corporation, 123 North Wacker Drive, Chicago, Illinois 60606,
Attention: Treasurer, and if to a holder, to the address of such holder set
forth in the security register or other records of the Trust or of the Debenture
Trustee under the Indenture, as the case may be, or to such other address as any
party may have furnished to the others in writing in accordance herewith, except
that notices of change of address shall be effective only upon receipt.

                                       22

 
     (d) Parties in Interest. All the terms and provisions of this Debenture
Exchange and Registration Rights Agreement shall be binding upon, shall inure to
the benefit of and shall be enforceable by the respective successors and assigns
of the parties hereto. In the event that any transferee of any holder of
Registrable Securities shall become a holder of Registrable Securities, in any
manner, whether by gift, bequest, purchase, operation of law or otherwise, such
transferee shall, without any further writing or action of any kind, be deemed a
party hereto for all purposes and such Registrable Securities shall be held
subject to all of the terms of this Debenture Exchange and Registration Rights
Agreement, and by taking and holding such Registrable Securities such transferee
shall be entitled to receive the benefits of and be conclusively deemed to have
agreed to be bound by and to perform all of the terms and provisions of this
Debenture Exchange and Registration Rights Agreement. If Aon shall so request,
any such successor, assign or transferee shall agree in writing to acquire and
hold the Registrable Securities subject to all of the terms hereof.

     (e) Survival. The respective indemnities, agreements, representations,
warranties and each other provision set forth in this Debenture Exchange and
Registration Rights Agreement or made pursuant hereto shall remain in full force
and effect regardless of any investigation (or statement as to the results
thereof) made by or on behalf of any holder of Registrable Securities, any
director, officer or partner of such holder, any agent or underwriter or any
director, officer or partner thereof, or any controlling person of any of the
foregoing, and shall survive delivery of and payment for the Registrable
Securities and the transfer and registration of Registrable Securities by such
holder and/or the consummation of an Exchange Offer.

     (f) LAW GOVERNING. THIS DEBENTURE EXCHANGE AND REGISTRATION RIGHTS
AGREEMENT SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF NEW YORK.

     (g) Headings. The descriptive headings of the several Sections and
paragraphs of this Debenture Exchange and Registration Rights Agreement are
inserted for convenience only, do not constitute a part of this Debenture
Exchange and Registration Rights Agreement and shall not affect in any way the
meaning or interpretation of this Debenture Exchange and Registration Rights
Agreement.

     (h) Entire Agreement; Amendments. This Debenture Exchange and Registration
Rights Agreement and the other agreements referred to herein or delivered
pursuant hereto which form a part hereof contain the entire understanding of the
parties with respect to its subject matter. This Debenture Exchange and
Registration Rights Agreement and such other agreements referred to herein
supersede all prior agreements and understandings between the parties with
respect to its subject matter. This Debenture Exchange and Registration Rights
Agreement may be amended and the observance of any term of this Debenture
Exchange and Registration Rights Agreement may be waived (either generally or in
a particular instance and either retroactively or prospectively) only by a
written instrument duly executed by Aon, the Trust and the holders of at least
66-2/3 percent in aggregate Liquidation Amount or principal amount, as the case
may be, of the Registrable Securities at the time outstanding. Each holder of
any Registrable Securities at the time or thereafter outstanding shall be bound

                                       23

 
by any amendment or waiver effected pursuant to this Section 9(h), whether or
not any notice, writing or marking indicating such amendment or waiver appears
on such Registrable Securities or is delivered to such holder.

     (i) Inspection. For so long as this Debenture Exchange and Registration
Rights Agreement shall be in effect, this Debenture Exchange and Registration
Rights Agreement and a complete list of the names and addresses of all the
registered holders of Registrable Securities shall be made available for
inspection and copying on any business day by any holder of Registrable
Securities at the offices of Aon at the address thereof set forth in Section
9(c) above.

     (j) Counterparts. This agreement may be executed by the parties in
counterparts, each of which shall be deemed to be an original, but all such
respective counterparts shall together constitute one and the same instrument.

     (k) Termination. Except for the respective indemnities, representations and
warranties set forth herein, this Debenture Exchange and Registration Rights
Agreement shall terminate when all Securities, Exchange Securities and
Registrable Securities cease to be outstanding.

                                       24

 
     This Debenture Exchange and Registration Rights Agreement is executed as of
the day and year first above written.

                               AON CORPORATION


                               By:  /s/ Harvey N. Medvin
                                        ----------------------------------
                                        Name:  Harvey N. Medvin
                                        Title: Executive Vice President, Chief
                                                 Financial Officer and Treasurer

                               AON CAPITAL A


                               By:  /s/ Harvey N. Medvin
                                   ----------------------------------------
                                        Name: Harvey N. Medvin
                                        Administrative Trustee


                               MORGAN STANLEY & CO. INCORPORATED
 
                               As Representative of the Purchasers named in
                               Schedule I to the Purchase Agreement


                               By:  /s/ Michael Fusco
                                    ----------------------------------------
                                        (Morgan Stanley & Co. Incorporated)

                               Acting severally, and not jointly and severally,
                               on behalf of themselves and each of the
                               Purchasers named in Schedule I to the Purchase
                               Agreement

                                       25