EXHIBIT 4.2


                          MORTGAGE LOAN PURCHASE AGREEMENT

            This Mortgage Loan Purchase Agreement (the "Agreement"), dated March
30, 2006, is between Banc of America Mortgage Securities, Inc., a Delaware
corporation (the "Purchaser" or the "Company") and Bank of America, National
Association, a national banking association ("BANA" or the "Seller").

            The Purchaser and the Seller hereby recite and agree as follows:

            1. Defined Terms. Terms used without definition herein shall have
the respective meanings assigned to them in the Pooling and Servicing Agreement
dated March 30, 2006 (the "Pooling and Servicing Agreement"), among the Company,
BANA, as servicer and Wells Fargo Bank, N.A., as trustee (the "Trustee"),
relating to the issuance of the Banc of America Alternative Loan Trust 2006-3
Mortgage Pass-Through Certificates, Series 2006-3 (the "Certificates") or, if
not defined therein, in the underwriting agreement dated March 27, 2006 (the
"Underwriting Agreement"), among the Company, BANA and Banc of America
Securities LLC (the "Underwriter") or in the purchase agreement dated March 30,
2006 (the "Purchase Agreement"), among the Company, BANA and Banc of America
Securities LLC.

            2. Purchase Price; Purchase and Sale. The Seller agrees to sell, and
the Company agrees to purchase, the mortgage loans (the "Mortgage Loans"),
listed in the Mortgage Loan Schedule. The purchase price (the "Purchase Price")
for the Mortgage Loans shall consist of $326,276,073.21 payable by the Company
to the Seller on the Closing Date in immediately available funds.

            Upon payment of the Purchase Price, the Seller shall be deemed to
have transferred, assigned, set over and otherwise conveyed to the Company all
the right, title and interest of the Seller in and to the Mortgage Loans,
including all interest and principal received or receivable by the Seller on or
with respect to the Mortgage Loans after the Cut-off Date (and including
scheduled payments of principal and interest due after the Cut-off Date but
received by the Seller on or before the Cut-off Date and Principal Prepayments
received or applied on the Cut-off Date, but not including payments of principal
and interest due on the Mortgage Loans on or before the Cut-off Date), together
with all of the Seller's rights, title and interest in and to the proceeds of
any related title, hazard, primary mortgage, mortgage pool policy or other
insurance policies, but excluding any fees payable by a Mortgagor for the right
to cancel any portion of principal or interest of a BPP Mortgage Loan. The
Company hereby directs the Seller, and the Seller hereby agrees, to deliver to
the Trustee all documents, instruments and agreements required to be delivered
by the Company to the Trustee under the Pooling and Servicing Agreement and such
other documents, instruments and agreements as the Company or the Trustee shall
reasonably request.

            3. Representations and Warranties. The Seller hereby represents and
warrants to the Company that (i) the Company's representations and warranties to
the Trustee pursuant to Section 2.04 of the Pooling and Servicing Agreement
insofar as they relate to the Mortgage Loans are true and correct, as of the
date thereof, and (ii) the Seller has not dealt with any broker, investment
banker, agent or other Person (other than the Company and Banc of America
Securities LLC) who may be entitled to any commission or compensation in
connection with the sale of the Mortgage Loans. The Seller hereby agrees to cure
any breach of such representations and warranties in accordance with the terms
of the Pooling and Servicing Agreement.

            4. Repurchase or Substitution. The Seller hereby agrees to
repurchase any Mortgage Loan (i) for which any document is not delivered, as
provided in paragraph 2 above, (ii) which is found by the Trustee to be
defective in any material respect, as provided in the Pooling and Servicing
Agreement, or (iii) which is discovered at any time not to be in conformance
with the representations and warranties referred to in paragraph 3 above and
which document relating thereto the Seller does not deliver or which defect or
breach the Seller does not cure (as provided in paragraph 3 above) within 90
days after the date of notice thereof from the Trustee or the Company, at a
price equal to the then unpaid principal balance thereof, plus accrued and
unpaid interest at the applicable Mortgage Interest Rate, through the last day
of the month in which such repurchase takes place. In addition, the Seller
hereby agrees to reimburse the Purchaser for any Reimbursement Amount.
Alternatively, the Seller hereby agrees, if so requested by the Company, to
substitute for any such Mortgage Loan, a new mortgage loan having
characteristics such that the representations and warranties referred to in
paragraph 3 above would not have been incorrect (except for representations and
warranties as to the correctness of the Mortgage Loan Schedule) had such
substitute mortgage loan originally been a Mortgage Loan. The Seller further
agrees that a substituted mortgage loan will have on the date of substitution
the criteria set forth in the definition of "Substitute Mortgage Loan" in the
Pooling and Servicing Agreement. The Seller shall remit to the Company, in cash,
the difference between the unpaid principal balance of the Mortgage Loan to be
substituted and the unpaid principal balance of the substitute mortgage loan.

            5. BPP Mortgage Loans. With respect to any BPP Mortgage Loan, the
Seller hereby agrees to remit to the Trustee, on behalf of the Trust, as
assignee of the Company (a) the amount of any principal and interest due by a
Mortgagor and cancelled for any month pursuant to the terms of the related
Mortgage Note (the "Monthly Covered Amount") upon the disability or involuntary
unemployment of the related Mortgagor or (b) the outstanding principal balance
of the Mortgage Loan cancelled pursuant to the terms of the related Mortgage
Note together with accrued interest at the Mortgage Interest Rate minus the
Servicing Fee Rate to the date of cancellation (the "Total Covered Amount") upon
the accidental death of the related Mortgagor. Any Monthly Covered Amount
payable by the Seller pursuant to clause (a) this Section 5 shall be deposited
by the Seller in the Servicer Custodial Account on or prior to, in the case of
the Monthly Covered Amount, the Remittance Date relating to the Distribution
Date immediately following the Due Date as to which such Monthly Covered Amount
relates and, in the case of a Total Covered Amount, the Remittance Date relating
to the Distribution Date in the month following the month in which the
cancellation to which such Total Covered Amount relates occurs.

            6. Underwriting. The Seller hereby agrees to furnish any and all
information, documents, certificates, letters or opinions with respect to the
mortgage loans, reasonably requested by the Company in order to perform any of
its obligations or satisfy any of the conditions on its part to be performed or
satisfied pursuant to the Underwriting Agreement or the Purchase Agreement at or
prior to the Closing Date.

            7. Costs. The Company shall pay all expenses incidental to the
performance of its obligations under the Underwriting Agreement and the Purchase
Agreement, including without limitation (i) any recording fees or fees for title
policy endorsements and continuations, (ii) the expenses of preparing, printing
and reproducing the Prospectus, the Prospectus Supplement, the Underwriting
Agreement, the Private Placement Memorandum, the Purchase Agreement, the Pooling
and Servicing Agreement and the Certificates and (iii) the cost of delivering
the Certificates to the offices of Banc of America Securities LLC insured to the
satisfaction of Banc of America Securities LLC.

            8. Notices. All demands, notices and communications hereunder shall
be in writing, shall be effective only upon receipt and shall, if sent to the
Company, be addressed to it at Banc of America Mortgage Securities, Inc., 214
North Tryon Street, Charlotte, North Carolina, 28255, Attention: General Counsel
with a copy to the Chief Financial Officer, or if sent to BANA, be addressed to
it at Bank of America, National Association, 101 South Tryon Street, Charlotte,
North Carolina, 28255, Attention: General Counsel with a copy to the Treasurer.

            9. Trustee Beneficiary. The representations, warranties and
agreements made by the Seller in this Agreement are made for the benefit of, and
may be enforced by, the Trustee and the Holders of Certificates to the same
extent that the Trustee and the Holders of Certificates, respectively, have
rights against the Company under the Pooling and Servicing Agreement in respect
of representations, warranties and agreements made by the Company therein.

            10. Recharacterization. The parties to this Agreement intend the
conveyance by the Seller to the Purchaser of all of its right, title and
interest in and to the Mortgage Loans pursuant to this Agreement to constitute a
purchase and sale and not a loan. Notwithstanding the foregoing, to the extent
that such conveyance is held not to constitute a sale under applicable law, it
is intended that this Agreement shall constitute a security agreement under
applicable law and that the Seller shall be deemed to have granted to the
Purchaser a first priority security interest in all of the Seller's right, title
and interest in and to the Mortgage Loans.

            11. Miscellaneous. This Agreement shall be governed by and construed
in accordance with the laws of the State of New York without regard to the
conflict of law provisions. Neither this Agreement nor any term hereof may be
changed, waived, discharged or terminated except by a writing signed by the
party against whom enforcement of such change, waiver, discharge or termination
is sought. This Agreement may not be changed in any manner which would have a
material adverse effect on Holders of Certificates without the prior written
consent of the Trustee. The Trustee shall be protected in consenting to any such
change to the same extent provided in Article IX of the Pooling and Servicing
Agreement. This Agreement may be signed in any number of counterparts, each of
which shall be deemed an original, which taken together shall constitute one and
the same instrument. This Agreement shall bind and inure to the benefit of and
be enforceable by the Company and the Seller and their respective successors and
assigns.



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            IN WITNESS WHEREOF, the Company and the Seller have caused this
Agreement to be duly executed by their respective officers as of the day and
year first above written.


                                       BANC OF AMERICA MORTGAGE SECURITIES,
                                       INC.




                                       By: /s/ Judy Lowman
                                           ----------------------------------
                                           Name:  Judy Lowman
                                           Title: Vice President


                                       BANK OF AMERICA, NATIONAL ASSOCIATION



                                       By: /s/ Vicki T. Cullen
                                           ----------------------------------
                                           Name:   Vicki T. Cullen
                                           Title:  Senior Vice President