<Page>

Filed by State Street Research Securities Trust
Pursuant to Rule 425 Under the Securities Act of 1933 and
Deemed filed pursuant to Rule 14a-2 of the
Securities Exchange Act of 1934
Subject Company: State Street Research Securities Trust
SEC File No. 33-74628

This filing relates to the proposed reorganizations of certain series of
State Street Research trusts ("State Street Research") into certain series of
the BlackRock Funds ("BlackRock") pursuant to Agreements and Plans of
Reorganization, forms of which are on file with the U.S. Securities and
Exchange Commission as appendices to the Combined Prospectus/Proxy Statements
on Form N-14 filed by BlackRock on November 8, 2004, and which are
incorporated by reference into this filing.

The following is a letter sent to shareholders of certain series of the
trusts reminding them to instruct the trusts on how to vote their shares.

                         ADJOURNED MEETING NOTICE

                                                              December 28, 2004


                        STATE STREET RESEARCH FUNDS

                         ADJOURNED MEETING NOTICE:
                         MEETING OF SHAREHOLDERS
                   HAS BEEN ADJOURNED TO JANUARY 24, 2005

Dear Shareholder:

We are writing to inform you that the Shareholder Meeting for your State
Street Research fund(s) has been adjourned to allow the fund(s) to solicit
additional votes.  The meeting has been adjourned to Monday, January 24, 2005
at 4:00 p.m. (Eastern Standard Time).  The fund(s) records indicate that you
were holding shares of the fund(s) and have not yet cast a vote.  Please take
the time now to cast your vote.  In order for your vote to be represented, we
must receive your instructions on or before the meeting on Monday, January
24, 2005.                    .

For your convenience, we have established four easy methods by which to cast
your vote:

     1. Vote by Telephone: with a live representative by calling
        1-877-288-6170 as soon as possible and have the enclosed proxy card
        in hand to provide our representatives with the information required
        to cast your vote.


<Page>


     2. Vote by Touch-Tone Telephone: by calling the toll-free number printed
        on your proxy card.

     3. Vote by Internet: by logging on to the web site address listed on
        your proxy card and following the instructions listed there.

     4. Vote by Mail: Complete and sign the enclosed proxy card and return by
        mail in the enclosed prepaid return envelope (if mailed in the United
        States).

As a shareholder, your vote is important.  If we do not receive your vote, a
representative of the fund or a third party solicitation firm may contact you
by telephone to obtain your vote.  We apologize if we have made multiple
requests to obtain your vote, but we want you to have every opportunity to
participate in this very important fund meeting.

If you have any questions about the proxy materials you received, please call
the number provided above or contact your financial advisor.

Sincerely,

/s/ Richard S. Davis

Richard S. Davis
Chairman of the Board
President & Chief Executive Officer


ADDITIONAL INFORMATION AND WHERE TO FIND IT BlackRock Funds ("BlackRock") has
filed Combined Prospectus / Proxy Statements with the Securities and Exchange
Commission Registration Statements, on Form N-14 (Nos. 333-119445,
333-119446, 333-119447, 333-119457, 333-119448, 333-119449, 333-119450,
333-119451, 333-119452, 333-119453, 333-119454, 333-119456, 333-119458,
333-119459 and 333-119461), of BlackRock and certain State Street Research
("SSR") funds and other relevant materials regarding the proposed
reorganizations (the "Reorganizations") of certain series of SSR trusts into
certain series of BlackRock. The Combined Prospectus/Proxy Statements were
sent to security holders of SSR funds seeking their approval of the
Reorganizations. WE URGE YOU TO READ THE COMBINED PROSPECTUS/PROXY STATEMENTS
FILED BY BLACKROCK WITH THE SEC ON NOVEMBER 8, 2004 AND THE OTHER RELEVANT
MATERIALS FILED BY BLACKROCK OR SSR WITH THE SEC BEFORE VOTING OR MAKING ANY
INVESTMENT DECISION WITH RESPECT TO THE REORGANIZATIONS, BECAUSE THEY CONTAIN
IMPORTANT INFORMATION ABOUT BLACKROCK, SSR AND THE REORGANIZATIONS. You may
obtain a free copy of these materials and other documents filed by BlackRock
or SSR with the SEC at the SEC's website at www.sec.gov. In addition, the
documents filed with the SEC by BlackRock may be obtained free of charge by
directing such request to: BlackRock Funds, Bellevue Park Corporate Center,
100 Bellevue Parkway, Wilmington, Delaware, 19809, (800) 441-7762. Documents
filed with the SEC by SSR may be obtained free of charge by directing such
request to: State Street Research, One Financial Center, Boston,
Massachusetts, 02111, (877) 773-8637.