The type-specific antigen of Group B Type II streptococci has been prepared free of other known cell components. This antigen is a capsular polysaccharide containing D-galactose, D-glucose, N-acetyl-D-glucosamine, and a labile component which has not been chemically characterized. Extraction of Type II streptococci with cold TCA yielded this antigen which contained two serological determinants. A partial antigen with only one of the determinants was obtained by extraction with dilute HCl at 100°C.
By means of the quantitative precipitin inhibition technique, a (ß-D-galactopyranoside has been established as the determinant of the HCl-extracted polysaccharide. The second determinant, present solely in the TCA antigen, has not been identified.