DNA sequencing of the gene encoding a complement-inhibiting protein of Streptococcus pyogenes (streptococcal inhibitor of complement, Sie) was carried out on 49 strains of S, pyogenes serotype M1. Those strains were obtained from patients and asymptomatic carriers in Japan from 1969 to 1997 and had various pulsed-field gel electrophoresis (PFGE) patterns. Four identical polymorphic sites were found in the strains with the same PFGE pattern (Ia), but not in those giving the pattern IIa. The other identical sites were found in the strains with the PFGE pattern IIa, but not in those with the pattern Ia, These observations suggest that each of PFGE patterns was restricted to a set of variation in the sic gene.