<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

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

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934

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

        Date of Report (Date of earliest event reported): October 3, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                 (ON BEHALF OF PREFERREDPLUS TRUST SERIES MSD-1)
             (Exact name of registrant as specified in its charter)

          DELAWARE             001-32019                    13-3891329
      (State or other        (Commission                (I. R. S. Employer
      jurisdiction  of        File Number)              Identification No.)
       incorporation)

   WORLD FINANCIAL CENTER,                                     10080
     NEW YORK,  NEW YORK                                    (Zip Code)
    (Address of principal
     executive offices)
                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT

SECTION 1.        REGISTRANT'S BUSINESS AND OPERATIONS

                  Not applicable.

SECTION 2.        FINANCIAL INFORMATION

                  Not applicable.

SECTION 3.        SECURITIES AND TRADING MARKETS

                  Not applicable.

SECTION 4.        MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

                  Not applicable.

SECTION 5.        CORPORATE GOVERNANCE AND MANAGEMENT

                  Not applicable.

SECTION 6.        [RESERVED]

SECTION 7.        REGULATION FD

                  Not applicable.
<PAGE>

SECTION 8.        OTHER EVENTS

   ITEM 8.01      OTHER EVENTS

           99.1   Distribution to holders of the PreferredPLUS Trust
                  Certificates Series MSD-1 on October 3, 2005.

                           For information with respect to the underlying
                   securities held by PreferredPLUS Trust Series MSD-1, please
                   refer to Morgan Stanley's (Commission file number 001-11758)
                   periodic reports, including annual reports on Form 10-K,
                   quarterly reports on Form 10-Q and current reports on Form
                   8-K, and other information on file with the Securities and
                   Exchange Commission (the "SEC"). You can read and copy these
                   reports and other information at the public reference
                   facilities maintained by the SEC at Room 1580, 100 F Street,
                   NE, Washington, D.C. 20549. You may obtain copies of this
                   material for a fee by writing to the SEC's Public Reference
                   Section of the SEC at 100 F Street, NE, Washington, D.C.
                   20549. You may obtain information about the operation of the
                   Public Reference Room by calling the SEC at 1-800-SEC-0330.
                   You can also access some of this information electronically
                   by means of the SEC's website on the Internet at
                   http://www.sec.gov, which contains reports, proxy and
                   information statements and other information that the
                   underlying securities issuer has filed electronically with
                   the SEC.

                           Although we have no reason to believe the information
                   concerning the underlying securities or the underlying
                   securities issuer contained in the underlying securities
                   issuer's Exchange Act reports is not reliable, neither the
                   depositor nor the trustee participated in the preparation of
                   such documents or made any due diligence inquiry with respect
                   to the information provided therein. No investigation with
                   respect to the underlying securities issuer (including,
                   without limitation, no investigation as to its financial
                   condition or creditworthiness) or of the underlying
                   securities has been made. You should obtain and evaluate the
                   same information concerning the underlying securities issuer
                   as you would obtain and evaluate if your investment were
                   directly in the underlying securities or in other securities
                   issued by the underlying securities issuer. There can be no
                   assurance that events affecting the underlying securities or
                   the underlying securities issuer have not occurred or have
                   not yet been publicly disclosed which would affect the
                   accuracy or completeness of the publicly available documents
                   described above.
<PAGE>

SECTION 9.         FINANCIAL STATEMENTS AND EXHIBITS

    ITEM 9.01      FINANCIAL STATEMENTS AND EXHIBITS

           (a)     Financial statements of business acquired.

                   Not Applicable.

           (b)     Pro forma financial information.

                   Not Applicable.

           (c)     Exhibits.

                   99.1           Trustee's report in respect of
                                  the October 3, 2005 distribution to holders
                                  of the PreferredPLUS Trust Certificates
                                  Series MSD-1.

<PAGE>

                                   SIGNATURES

                  Pursuant to the requirements of the Securities Exchange Act of
                  1934, the registrant has duly caused this report to be signed
                  on its behalf by the undersigned, hereunto duly authorized.


                                       MERRILL LYNCH DEPOSITOR, INC.

         Date: October 12, 2005        By:    /s/ Zvi Gillon
                                              -------------------------------
                                       Name:  Zvi Gillon
                                       Title: Vice President




<PAGE>



                                            EXHIBIT INDEX


                 99.1      Trustee's report in respect of the October 3,
                           2005 distribution to holders of the PreferredPLUS
                           Trust Certificates Series MSD-1.
[{"type": "8-K", "sequence": "1", "filename": "b409176_8k.txt", "description": "CURRENT REPORT", "secsgml_size_bytes": 6596}]
{"company-data": {"conformed-name": "PREFERREDPLUS TRUST SERIES MSD-1", "cik": "0001173925", "assigned-sic": "6189", "irs-number": "000000000", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "8-K", "act": "34", "file-number": "001-32019", "film-number": "051134465"}, "business-address": {"street1": "4 WORLD FINANCIAL CENTER", "street2": "NORTH TOWER 7TH FL", "city": "NEW YORK", "state": "NY", "zip": "10080", "phone": "2124491000"}, "mail-address": {"street1": "4 WORLD FINANCIAL CENTER", "street2": "NORTH TOWER 7TH FL.", "city": "NEW YORK", "state": "NY", "zip": "10080"}}
SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

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

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       The Securities Exchange Act of 1934

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

        Date of Report (Date of earliest event reported): October 3, 2005

                          MERRILL LYNCH DEPOSITOR, INC.
                 (ON BEHALF OF PREFERREDPLUS TRUST SERIES MSD-1)
             (Exact name of registrant as specified in its charter)

          DELAWARE             001-32019                    13-3891329
      (State or other        (Commission                (I. R. S. Employer
      jurisdiction  of        File Number)              Identification No.)
       incorporation)

   WORLD FINANCIAL CENTER,                                     10080
     NEW YORK,  NEW YORK                                    (Zip Code)
    (Address of principal
     executive offices)
                           --------------------------

       Registrant's telephone number, including area code: (212) 449-1000

                      INFORMATION TO BE INCLUDED IN REPORT

SECTION 1.        REGISTRANT'S BUSINESS AND OPERATIONS

                  Not applicable.

SECTION 2.        FINANCIAL INFORMATION

                  Not applicable.

SECTION 3.        SECURITIES AND TRADING MARKETS

                  Not applicable.

SECTION 4.        MATTERS RELATED TO ACCOUNTANTS AND FINANCIAL STATEMENTS

                  Not applicable.

SECTION 5.        CORPORATE GOVERNANCE AND MANAGEMENT

                  Not applicable.

SECTION 6.        [RESERVED]

SECTION 7.        REGULATION FD

                  Not applicable.
SECTION 8.        OTHER EVENTS

   ITEM 8.01      OTHER EVENTS

           99.1   Distribution to holders of the PreferredPLUS Trust
                  Certificates Series MSD-1 on October 3, 2005.

                           For information with respect to the underlying
                   securities held by PreferredPLUS Trust Series MSD-1, please
                   refer to Morgan Stanley's (Commission file number 001-11758)
                   periodic reports, including annual reports on Form 10-K,
                   quarterly reports on Form 10-Q and current reports on Form
                   8-K, and other information on file with the Securities and
                   Exchange Commission (the "SEC"). You can read and copy these
                   reports and other information at the public reference
                   facilities maintained by the SEC at Room 1580, 100 F Street,
                   NE, Washington, D.C. 20549. You may obtain copies of this
                   material for a fee by writing to the SEC's Public Reference
                   Section of the SEC at 100 F Street, NE, Washington, D.C.
                   20549. You may obtain information about the operation of the
                   Public Reference Room by calling the SEC at 1-800-SEC-0330.
                   You can also access some of this information electronically
                   by means of the SEC's website on the Internet at
                   http://www.sec.gov, which contains reports, proxy and
                   information statements and other information that the
                   underlying securities issuer has filed electronically with
                   the SEC.

                           Although we have no reason to believe the information
                   concerning the underlying securities or the underlying
                   securities issuer contained in the underlying securities
                   issuer's Exchange Act reports is not reliable, neither the
                   depositor nor the trustee participated in the preparation of
                   such documents or made any due diligence inquiry with respect
                   to the information provided therein. No investigation with
                   respect to the underlying securities issuer (including,
                   without limitation, no investigation as to its financial
                   condition or creditworthiness) or of the underlying
                   securities has been made. You should obtain and evaluate the
                   same information concerning the underlying securities issuer
                   as you would obtain and evaluate if your investment were
                   directly in the underlying securities or in other securities
                   issued by the underlying securities issuer. There can be no
                   assurance that events affecting the underlying securities or
                   the underlying securities issuer have not occurred or have
                   not yet been publicly disclosed which would affect the
                   accuracy or completeness of the publicly available documents
                   described above.
SECTION 9.         FINANCIAL STATEMENTS AND EXHIBITS

    ITEM 9.01      FINANCIAL STATEMENTS AND EXHIBITS

           (a)     Financial statements of business acquired.

                   Not Applicable.

           (b)     Pro forma financial information.

                   Not Applicable.

           (c)     Exhibits.

                   99.1           Trustee's report in respect of
                                  the October 3, 2005 distribution to holders
                                  of the PreferredPLUS Trust Certificates
                                  Series MSD-1.
SIGNATURES

                  Pursuant to the requirements of the Securities Exchange Act of
                  1934, the registrant has duly caused this report to be signed
                  on its behalf by the undersigned, hereunto duly authorized.

                                       MERRILL LYNCH DEPOSITOR, INC.

         Date: October 12, 2005        By:    /s/ Zvi Gillon
                                              -------------------------------
                                       Name:  Zvi Gillon
                                       Title: Vice President
EXHIBIT INDEX

                 99.1      Trustee's report in respect of the October 3,
                           2005 distribution to holders of the PreferredPLUS
                           Trust Certificates Series MSD-1.