56 strains of Streptococcus mutans, comprising organisms from various laboratory culture collections and some original isolates, were examined by cell wall carbohydrate chromatography. Three patterns of reducing sugars were detected: pattern 1, glucose, galactose and rhamnose; pattern 2, galactose and rhamnose, and pattern 3, glucose and rhamnose. 14 strains fell into pattern 1, four strains into pattern 2, and 38 strains into pattern 3. Cell wall agglutination tests using antisera prepared against strains representative of the five serotypes of Strep. mutans allowed further subdivision of organisms with cell wall patterns 1 and 3. Strains of cell wall pattern 2 fell into a clearly defined group of strains of serotype b. Pattern 3 included examples of serotype c and e, and type specific sera could be produced by cross-absorption with cell walls. Pattern 1 strains included serotype a and d; serotype a strains could be separated using cross-absorbed sera, but strains resembling serotype d appeared to be more heterogeneous. The results indicate that for Strep. mutans serotypes a, b, c and e at least one of the type antigens, probably carbohydrate, is located in trypsin-treated cell walls. The type d antigen or antigens which have previously been demonstrated by immunofluorescence do not appear to be associated with trypsinized cell walls, and further subdivisions of the serotype d strains was possible upon the basis of cell wall agglutination tests.