UNITED STATES

                      SECURITIES AND EXCHANGE COMMISSION

                             WASHINGTON, D.C. 20549


                                  SCHEDULE 13G
                   UNDER THE SECURITIES AND EXCHANGE ACT OF 1934

                         American Caresource Holdings, Inc.
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                                 (Name of Issuer)

                     Common Stock, par value $.001 per share
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                          (Title of Class of Securities)

                                 02505A 10 3
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                                 (CUSIP No.)

                                December 20, 2005
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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(b)
[X] Rule 13d-1(c)
[  ]  Rule 13d-1(d)





CUSIP No. 141653105

1.   Names of Reporting  Persons,  I.R.S.  Identification  Nos. of above persons
     (entities only).

Principal Financial Group, Inc.
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2.  Check the Appropriate Box if a Member of a Group (See Instructions)

(a)  [X]

(b)  [  ]

3.  SEC Use Only

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4.  Citizenship or Place of Organization

                        Delaware
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                                         5.  Sole Voting Power

                                                     0
                                         --------------------------------------

NUMBER OF                                6.  Shared Voting Power
SHARES
BENEFICIALLY                                      1,872,675
OWNED BY                                 --------------------------------------
EACH
REPORTING                                7.  Sole Dispositive Power
PERSON WITH
                                                     0
                                         --------------------------------------

                                         8.  Shared Dispositive Power

                                                  1,872,675
                                         --------------------------------------

9.  Aggregate Amount Beneficially Owned by Each Reporting Person

                   1,872,675
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10.  Check Box if the Aggregate Amount in Row (11) Excludes Certain Shares

                                [  ]

11.  Percent of Class Represented by Amount in Row (11)

                     15.1%
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                                       2


12.  Type of Reporting Person

                     HC
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1. Names of  Reporting  Persons,  I.R.S.  Identification  Nos. of above  persons
(entities only).

Principal Financial Services, Inc.
-------------------------------------------------------------------------------

2.  Check the Appropriate Box if a Member of a Group (See Instructions)

(a)  [X]

(b)  [  ]

3.  SEC Use Only

-------------------------------------------------------------------------------

4.  Citizenship or Place of Organization

                                    Iowa
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                                        5.  Sole Voting Power

NUMBER OF                                            0
SHARES                                  ---------------------------------------
BENEFICIALLY
OWNED BY                                6.  Shared Voting Power
EACH
REPORTING                                          1,872,675
PERSON WITH                             ---------------------------------------

                                        7.  Sole Dispositive Power

                                                     0
                                        ---------------------------------------

                                        8.  Shared Dispositive Power

                                                  1,872,675
                                        ---------------------------------------

9.  Aggregate Amount Beneficially Owned by Each Reporting Person

                          1,872,675
-------------------------------------------------------------------------------

10.  Check Box if the Aggregate Amount in Row (11) Excludes Certain Shares

                            [  ]

                                       3


11.  Percent of Class Represented by Amount in Row (11)

                           15.1%
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12.  Type of Reporting Person

                            HC
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1. Names of  Reporting  Persons,  I.R.S.  Identification  Nos. of above  persons
(entities only).

Principal Life Insurance Company
-------------------------------------------------------------------------------

2.  Check the Appropriate Box if a Member of a Group (See Instructions)

(a)  [X]

(b)  [  ]

3.  SEC Use Only

-------------------------------------------------------------------------------

4.  Citizenship or Place of Organization

                                Iowa
-------------------------------------------------------------------------------

                                      5.  Sole Voting Power

                                                    0
                                      -----------------------------------------
NUMBER OF                             6.  Shared Voting Power
SHARES
BENEFICIALLY                                    1,872,675
OWNED BY                              -----------------------------------------
EACH
REPORTING                             7.  Sole Dispositive Power
PERSON WITH
                                                    0
                                      -----------------------------------------

                                      8.  Shared Dispositive Power

                                               1,872,675
                                      -----------------------------------------

9.  Aggregate Amount Beneficially Owned by Each Reporting Person

                       1,872,675
-------------------------------------------------------------------------------

                                       4


10.  Check Box if the Aggregate Amount in Row (11) Excludes Certain Shares

                          [  ]

11.  Percent of Class Represented by Amount in Row (11)

                          15.1%
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12.  Type of Reporting Person

                           IC
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ITEM 1.  ISSUER.

The issuer is American  Caresource  Holdings,  Inc., whose principal offices are
located at 8080 Tri-Star Drive, Suite 100, Irving, Texas 75063.

ITEM 2.  IDENTITY AND BACKGROUND.

This statement  relates to shares of Common Stock, par value $.001 per share, of
American  Caresource  Holdings,  Inc.,  CUSIP No. 02505A 10 3. This statement is
being filed by: (i) Principal  Financial  Group,  Inc.  ("PFG"),  (ii) Principal
Financial Services, Inc. ("PFS") and Principal Life Insurance Company ("PLIC").

PFG is a corporation  incorporated under the laws of the State of Delaware.  Its
common stock is publicly  traded on the New York Stock Exchange under the ticker
symbol PFG. PFG is a holding company.  The address of its principal business and
principal office is 711 High Street, Des Moines, Iowa 50392.

PFS, an Iowa  corporation,  is a  wholly-owned  subsidiary  of PFG and a holding
company.  Its  principal  business and  principal  office is located at 711 High
Street, Des Moines, Iowa 50392.

PLIC is a stock insurance company organized under the laws of the State of Iowa.
The  principal  business  activity  of PLIC is the  provision  of  products  and
services for businesses,  groups and individuals including individual insurance,
pension plans and group/employee benefits. The address of its principal business
and principal office is 711 High Street, Des Moines, Iowa 50392.

By virtue of their  ownership and control of PLIC, PFG and PFS have the ultimate
voting and dispositive  power with respect to the shares of American  Caresource
Holdings Common Stock held by PLIC and may be deemed indirect  beneficial owners
of all the shares of American  Caresource  Holdings  Common  Stock owned by PLIC
within the meaning of Rule 13d-3(a) under the  Securities  Exchange Act of 1934,
as amended (the "Act").

ITEM 3.  NOT APPLICABLE.

ITEM 4.  OWNERSHIP.



                                       5


Provide the following  information regarding the aggregate number and percentage
of the class of securities of the issuer identified in Item 1.

   (a)  Amount beneficially owned:      1,872,675       .

   (b)  Percent of class:        15.1                   .

   (c)  Number of shares as to which the person has:

       (i)   Sole power to vote or to direct the vote               .

       (ii)  Shared power to vote or to direct the vote    1,872,675       .

       (iii) Sole power to dispose or to direct the disposition of          .

       (iv)  Shared power to dispose or to direct the disposition of 1,872,675 .

ITEM 5.  NOT APPLICABLE.

ITEM 6.  NOT APPLICABLE.

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


                              See Item 2.

ITEM 8.  SEE EXHIBIT A.

ITEM 9.  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 not acquired and are not held for the
     purpose of or with the effect of changing or influencing the control of the
     issuer  of the  securities  and  were  not  acquired  and are  not  held in
     connection with or as a participant in any transaction  having that purpose
     or effect.

                                       6



                                   SIGNATURES


After reasonable inquiry and to the best of the Reporting Person's knowledge and
belief,  the Reporting  Person  certifies that the information set forth in this
statement    is   true,    complete    and    correct.

December 29, 2005
-------------------------------------------------------------------------------
Date

PRINCIPAL FINANCIAL GROUP, INC.

By:   /s/ Joyce N. Hoffman
     -----------------------

        Joyce N. Hoffman

        Senior Vice President & Corporate Secretary
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Signature

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December 29, 2005
-------------------------------------------------------------------------------
Date

PRINCIPAL FINANCIAL SERVICES, INC.

By:   /s/ Joyce N. Hoffman
     -----------------------

        Joyce N. Hoffman

        Senior Vice President & Corporate Secretary
-------------------------------------------------------------------------------
Signature

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December 29, 2005
-------------------------------------------------------------------------------
Date

PRINCIPAL LIFE INSURANCE COMPANY

By:   /s/ Joyce N. Hoffman
     -----------------------

        Joyce N. Hoffman

        Senior Vice President & Corporate Secretary
-------------------------------------------------------------------------------
Signature

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Name/Title


                                       7




                                EXHIBIT A

                        Joint Filing Agreement



     In accordance with Rule 13d-1(f) under the Securities Exchange Act of 1934,
as amended,  each of the parties  hereto  agrees with the other parties that the
statement  of  Schedule  13G  pertaining  to  certain   securities  of  American
Caresource Holdings,  Inc. to which this agreement is an exhibit is filed by and
on behalf of each such  party and that any  amendment  thereto  will be filed on
behalf of each such party.

Dated:   December 29, 2005

                                        PRINCIPAL FINANCIAL GROUP, INC.



                                        By:      ______________________________

                                                 Joyce N. Hoffman

                                                 Senior Vice President &

                                                 Corporate Secretary



                                        PRINCIPAL FINANCIAL SERVICES,

                                        INC.

                                        By:      ______________________________

                                                 Joyce N. Hoffman

                                                 Senior Vice President &

                                                 Corporate Secretary



                                       8


                                        PRINCIPAL LIFE INSURANCE

                                        COMPANY



                                        By:      ______________________________

                                                 Joyce N. Hoffman

                                                 Senior Vice President &

                                                 Corporate Secretary