MFS SERIES TRUST X, 497, 1999-03-01

MFS SERIES TRUST X
497, 1999-03-01

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                        MFS(R) EMERGING MARKETS DEBT FUND

                      Supplement to the Current Prospectus



         The  description  of portfolio  managers  under the  "Management of the
Funds - Investment Adviser" section is hereby restated as follows:

Emerging  Markets  Debt Fund - The  portfolio  manager of the Fund is Matthew W.
                               Ryan, a Vice President of MFS. Mr. Ryan has been 
                               employed as a  portfolio  manager of the Fund
                               since July 24, 1998 and as an analyst by the
                               Adviser since April 1997. From July 1993 to 
                               March 1997,  Mr.  Ryan  worked as an  economist
                               with   the  U.S.   Executive   Director's Office
                               of  the International  Monetary  Fund.  Mr. Ryan
                               is also a Chartered Financial Analyst.












                The date of this Supplement is February 25, 1999.