<PAGE>

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D. C. 20549

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

                                    FORM 10-K

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

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

            For the fiscal year ended:          Commission file number:
                 DECEMBER 31, 2003                   333-68854-02

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

                    DELAWARE                         13-3891329
                 (State or other                 (I. R. S. Employer
                 jurisdiction of                 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

Securities registered pursuant to Section 12(b) of the Act:

PREFERREDPLUS TRUST CERTIFICATES, SERIES ALL-1, LISTED ON THE NEW YORK STOCK
EXCHANGE

Securities registered pursuant to Section 12(g) of the Act: NOT APPLICABLE

Indicate by check mark whether the Registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the Registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days.
                                 Yes [X] No [ ]

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this form 10-K or any amendment to this
form 10-K.[X]

<PAGE>

Indicate by check mark whether the registrant is an accelerated filer (as
defined in Rule 12b-2 of the Act).        Yes [ ]     No [X]

State the aggregate market value of the voting and non-voting common equity held
by non-affiliates of the registrant. The aggregate market value shall be
computed by reference to the price at which the common equity was sold, or the
average bid and asked prices of such common equity, as of the last business day
of the registrant's most recently completed second fiscal quarter.

                                 NOT APPLICABLE

Indicate the number of shares outstanding for each of the registrant's class of
common stock, as of the latest practicable date.

                                 NOT APPLICABLE

                       Documents Incorporated by Reference

                                      NONE

PART I.

ITEM 1.           BUSINESS.

                  None.

ITEM 2.           PROPERTIES.

                  None.

ITEM 3.           LEGAL PROCEEDINGS.

                  None.

ITEM 4.           SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS.

                  None.

PART II.

ITEM 5.           MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED STOCKHOLDER
                  MATTERS.

                  The Trust Certificates issued by PreferredPlus Trust Series
                  ALL-1 are represented by one or more physical certificates
                  registered in the name of Cede & Co., the nominee of the
                  Depository Trust Company.

                  The Trust Certificates are listed on the New York Stock
                  Exchange.

<PAGE>

ITEM 6.           SELECTED FINANCIAL DATA.

                  Not Applicable.

ITEM 7.           MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION
                  AND RESULTS OF OPERATIONS.

                  Not Applicable.

ITEM 7A.          QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

                  Not Applicable.

ITEM 8.           FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA.

                  Not Applicable.

ITEM 9.           CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING
                  AND FINANCIAL DISCLOSURE.

                  Not Applicable.

PART III.

ITEM 10.          DIRECTORS AND EXECUTIVE OFFICERS OF THE REGISTRANT.

                  Not Applicable.

ITEM 11.          EXECUTIVE COMPENSATION.

                  Not Applicable.

ITEM 12.          SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
                  AND RELATED STOCKHOLDER MATTERS.

                  (a)      None.

                  (b)      Not Applicable.

                  (c)      Not Applicable.

ITEM 13.          CERTAIN RELATIONSHIPS AND RELATED PARTY TRANSACTIONS.

                  None.

ITEM 14.          CONTROLS AND PROCEDURES.

                  Not Applicable.

<PAGE>

PART IV.

ITEM 15.          EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS OF FORM
                  8K.

                  Trustee's report in respect of the Feb 15, 2003 distribution
                  to holders of the PreferredPlus Trust Series ALL-1 Class A
                  Certificates incorporated herein by reference as exhibits to
                  Registrant's Current Report on Form 8K filed with the
                  Securities and Exchange Commission on April 17, 2003.

                  Trustee's report in respect of the August 15, 2003
                  distribution to holders of the PreferredPlus Trust Series
                  ALL-1 Class A Certificates incorporated herein by reference as
                  exhibits to Registrant's Current Report on Form 8K filed with
                  the Securities and Exchange Commission on August 26, 2003.

                                   SIGNATURES

                  Pursuant to the requirements of Section 13 or 15(d) 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: 1/23/04                 By: /s/ Barry Finkelstein
                                                Name: Barry Finkelstein
                                                Title: President

<PAGE>

I, Barry N. Finkelstein, certify that:

1. I have reviewed this annual report on Form 10-K, and all reports on Form 8-K
containing distribution or servicing reports filed in respect of periods
included in the year covered by this annual report, of Merrill Lynch Depositor,
Inc.;

2. Based on my knowledge, the information in these reports, taken as a whole,
does not contain any untrue statement of a material fact or omit to state a
material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading as of the
last day of the period covered by this annual report;

3. Based on my knowledge, the distribution or servicing information required to
be provided to the depositor by the trustee under the pooling and servicing, or
similar, agreement, for inclusion in these reports is included in these reports;
and

4. I am responsible for reviewing the activities performed by the depositor and
the trustee under the pooling and servicing, or similar, agreement and based
upon my knowledge and the annual compliance review required under that
agreement, and except as disclosed in the reports, the depositor and trustee
have each fulfilled its obligations under that agreement.

In giving the certifications above, I have reasonably relied on information
provided to me by the following unaffiliated parties: The Bank of New York and
its officers and agents.

Date: 1/23/04

/s/ Barry N. Finkelstein
Barry N. Finkelstein
Chief Executive Officer