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                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 13G

                                 AMENDMENT NO 1

                    UNDER THE SECURITIES EXCHANGE ACT OF 1934


                          AmerisourceBergen Corporation
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                                (Name of Issuer)


                           Common Stock, no par value
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                         (Title of Class of Securities)


                                    03073E105
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                                 (CUSIP Number)


                                 April 30, 2006
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             (Date of Event which Requires Filing of this Statement)


Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

        [ ] Rule 13d-1(c)      [ ] Rule 13d-1(d)      [X] Rule 13d-1(b)


* The remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act") or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).

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--------------------------                            --------------------------
CUSIP NO.  03073E105              SCHEDULE 13G                 PAGE 2 OF 6 PAGES
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1.                NAME OF REPORTING PERSON/S.S. OR I.R.S. IDENTIFICATION
                  NO. OF ABOVE PERSON

                  PZENA INVESTMENT MANAGEMENT, LLC
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2.                CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP    (A) [ ]
                                                                      (B) [ ]
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3.                SEC USE ONLY


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4.                CITIZENSHIP OR PLACE OF ORGANIZATION

                  DELAWARE
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                               5.     SOLE VOTING POWER

                                      4,308,950
   NUMBER OF                  --------------------------------------------------
    SHARES                     6.     SHARED VOTING POWER
 BENEFICIALLY
   OWNED BY                           0
    EACH                      --------------------------------------------------
  REPORTING                    7.     SOLE DISPOSITIVE POWER
   PERSON
    WITH:                             9,704,475
                              --------------------------------------------------
                               8.     SHARED DISPOSITIVE POWER

                                      0
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9.                AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

                  9,704,475
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10.               CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
                  CERTAIN SHARES*                                          [ ]
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11.               PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

                  4.64%
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12.               TYPE OF REPORTING PERSON*

                  IA
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CUSIP NO. 03073E105               SCHEDULE 13G                 PAGE 3 OF 6 PAGES
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ITEM 1.

      (a) Name of Issuer:    AmerisourceBergen Corp.
                         -------------------------------

      (b) Address of Issuer's Principal Executive Offices:

                   1300 Morris Drive, Chesterbrook, PA 19087
                   -------------------------------------------

ITEM 2.

      (a) Name of Person Filing: Pzena Investment Management, LLC
                                ------------------------------------------------
      (b) Address of Principal Business Office or, if none, Residence:

              120 West 45th Street, 20th Floor, New York, NY 10036
             ------------------------------------------------------

      (c) Citizenship:    Delaware
                      ---------------------

     (d) Title of Class of Securities:   Common Stock
                                      -------------------

      (e) CUSIP Number:   03073E105
                       -----------------

ITEM 3. IF THIS STATEMENT IS FILED PURSUANT TO RULE 13D-1(B), OR 13D-2(B), CHECK
        WHETHER THE PERSON FILING IS A:

     (a)  [ ] Broker or Dealer registered under Section 15 of the Act
     (b)  [ ] Bank as defined in section 3(a)(6) of the Act
     (c)  [ ] Insurance Company as defined in section 3(a)(19) of the Act
     (d)  [ ] Investment  Company  registered  under section 8 of the Investment
              Company Act of 1940
     (e)  [X] Investment  Adviser registered under section 203 of the Investment
              Advisers Act or under the laws of any State
     (f)  [ ] Employee  Benefit  Plan,  Pension  fund  which is  subject to the
              provisions of the Employee  Retirement  Income Security Act of
              1974 or Endowment Fund; see Section 240.13d-1(b)(1)(ii)(F)
     (g)  [ ] Parent Holding Company, in accordance with Section 240.13d-1(b)
              (ii)(G)(Note: See Item 7)
     (h)  [ ] A Savings  Association  as defined in Section  3(b) of the Federal
              Deposit Insurance Act
     (i)  [ ] A  Church  Plan  that  is  excluded  from  the  definition  of  an
              investment  company under Section  3(c)(14) of the Investment
              Company Act of 1940
     (j)  [ ] Group, in accordance with Section 240.13d-1(b)(1)(ii)(J)

If this statement is filed pursuant to Rule 240.13d-1(c),  check this box [ ].



CUSIP NO. 03073E105                SCHEDULE 13G                PAGE 4 OF 6 PAGES
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ITEM 4.   OWNERSHIP

If the percent of the class owned, as of December 31 of the year covered by this
statement, or as of the last day of any month described in Rule 13d-1(b)(2),  if
applicable,  exceeds five percent,  provide the following information as of that
date and identify those shares which there is a right to acquire.

(a) Amount Beneficially Owned:     9,704,475
                              --------------------------------------------------
(b) Percent of Class:       4.64%
                       ---------------------------------------------------------
(c) Number of shares as to which such person has:

     (i)sole power to vote or to direct the vote:      4,308,950
                                                   -----------------------------
    (ii)shared power to vote or to direct the vote:     0
                                                    ----------------------------
   (iii)sole power to dispose or to direct the disposition of:    9,704,475
                                                              ------------------
    (iv) shared power to dispose or to direct the disposition of: 0
                                                                 ---------------

ITEM 5.   OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

If this  statement  is being filed to report the fact that as of the date hereof
the  reporting  person has ceased to be the  beneficial  owner of more than five
percent of the class of securities, check the following [X].


ITEM 6.   OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

If any other person is known to have the right to receive or the power to direct
the  receipt  of  dividends  from,  or the  proceeds  from  the  sale  of,  such
securities,  a statement  to that effect  should be included in response to this
item and, if such interest relates to more than five percent of the class,  such
person  should be  identified.  A listing of the  shareholders  of an investment
company registered under the Investment Company Act of 1940 or the beneficiaries
of employees benefit plan, pension fund or endowment fund is not required.

CLIENTS  OF THE FILING  INVESTMENT  MANAGER  HAVE THE RIGHT TO  RECEIVE  AND THE
ULTIMATE POWER TO DIRECT THE RECEIPT OF DIVIDENDS  FROM, OR THE PROCEEDS OF SALE
OF THE  SECURITIES  REPORTED  ON  HEREINABOVE.  NO  INTEREST  OF ANY ONE OF SUCH
CLIENTS RELATES TO MORE THAN FIVE PERCENT OF THE CLASS.


ITEM 7.  IDENTIFICATION  AND CLASSIFICATION OF THE SUBSIDIARY WHICH ACQUIRED THE
         SECURITY BEING REPORTED ON BY THE PARENT HOLDING COMPANY

If  a  parent  holding  company  has  filed  this  schedule,  pursuant  to  Rule
13d-1(b)(ii)(G),  so indicate under Item 3(g) and attach an exhibit  stating the
identity and the Item 3 classification of the relevant  subsidiary.  If a parent
holding  company has filed this schedule  pursuant to Rule  13d-1(c),  attach an
exhibit stating the identification of the relevant subsidiary. NOT APPLICABLE.




CUSIP NO. 03073E105                SCHEDULE 13G                PAGE 5 OF 6 PAGES
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ITEM 8.   IDENTIFICATION AND CLASSIFICATION OF MEMBERS OF THE GROUP

If a group has filed this schedule pursuant to Rule 13d-1(b)(ii)(J), so indicate
under  Item  3(h)  and  attach  an  exhibit  stating  the  identity  and  Item 3
classification  of each member of the group.  If a group has filed this schedule
pursuant to Rule 13d-1(d), attach an exhibit stating the identity of each member
of the group. NOT APPLICABLE.


ITEM 9.   NOTICE OF DISSOLUTION OF GROUP

Notice of dissolution of a group may be furnished as an exhibit stating the date
of the  dissolution and that all further filings with respect to transactions in
the security report on will be filed,  if required,  by members of the group, in
their individual capacity. NOT APPLICABLE.


ITEM 10.  CERTIFICATION

By signing  below,  I certify that, to the best of my knowledge and belief,  the
securities  referred to above were acquired and are held in the ordinary  course
of business and were not acquired and are not held for the purpose of and do not
have the effect of  changing  or  influencing  the control of the issuer of such
securities  and were not  acquired and are not held in  connection  with or as a
participant in any transaction having that purpose or effect.





CUSIP NO. 03073E105                SCHEDULE 13G                PAGE 6 OF 6 PAGES
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                                    SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I hereby
certify that the information set forth in this statement is true, complete and
correct.





Dated as of May 9, 2006



Richard S. Pzena, Manager
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NAME/TITLE