MERRILL LYNCH MUNICIPAL BOND FUND, INC.

                     SUPPLEMENT DATED JANUARY 11, 2000 TO THE

                        PROSPECTUS DATED OCTOBER 29, 1999

         A new portfolio manager has been assigned to the Insured Portfolio of
the Merrill Lynch Municipal Bond Fund, Inc.

         The section "Details About the Fund--Insured Portfolio" on page 16
of the Prospectus is amended by revising the sidebar section "About the
Portfolio Manager of the Insured Portfolio" replacing the biographical
information therein with respect to the prior portfolio manager, Mr. Jacobs,
with the following regarding the new portfolio manager, Mr. DiMella:

         Robert A. DiMella is a Vice President of the Investment Adviser and
Vice President and portfolio manager of the Insured Portfolio.  Mr. DiMella
has been a Vice President of Merrill Lynch Asset  Management  since 1997 and was
an Assistant  Vice  President  from 1995 to 1997. He was an Assistant  Portfolio
Manager of Merrill Lynch Asset Management from 1993 to 1995.




                     MERRILL LYNCH MUNICIPAL BOND FUND, INC.

                     SUPPLEMENT DATED JANUARY 11, 2000 TO THE
           STATEMENT OF ADDITIONAL INFORMATION DATED OCTOBER 29, 1999

A new  portfolio  manager  has been  assigned to the  Insured  Portfolio  of the
Merrill Lynch Municipal Bond Fund, Inc.

Page 15 of the Statement of Additional Information, under the heading MANAGEMENT
OF THE FUND, is  supplemented  by adding the following  after the description of
Donald C. Burke:

     ROBERT A. DIMELLA, CFA (33) - Vice President and Portfolio  Manager(1)(2) -
Vice President of MLAM since 1997; Assistant Vice President of MLAM from 1995 to
1997; Assistant Portfolio Manager of MLAM from 1993 to 1995.