Cell-free supernatant of Streptococcus mutans cultures was concentrated by 50% ammonium sulphate precipitation to 1/50 of the original culture volume. Most extracellular glucosyltransferase activity was detected in the supernatant. Furthermore, the supernatant reacted with serotype specific antiserum, showing immunological identities with the serotype specific polysaccharide antigen obtained from whole cells by hot saline or NaOH extraction in double diffusion tests. Immunoelectrophoretic analysis also revealed that the supernatant antigen possessed significant quantities of lipid-bound and free glycerol teichoic acid antigens. The lipoteichoic acid (LTA) was obtained from whole cells by phenol-water extraction. The lipid-teichoic acid linkage was easily split by mild acid or alkaline hydrolysis. The supernatant and phenol antigens spontaneously sensitized sheep red blood cells. These antigens were adsorbed to hydroxyapatite powder. The extracellular LTA and glucosyltransferase were found to be closely associated and difficult to separate chromatographically. In vivo significance of these properties of LTA and GTase is discussed in terms of the ecology of S. mutans and other oral streptococci.