Purified cell walls of Actinomyces viscosus and Actinomyces naeslundii were solubilized by the enzymatic action of M1 N-acetylmuramidase. Soluble cell wall carbohydrate antigens were purified by column chromatography. A purified antigen preparation (fraction C) from A. viscosus ATCC 19246 was found to contain deoxyhexoses (rhamnose and 6-deoxytalose), hexosse (galactose, glucose and mannose), and a peptidoglycan component. This preparation gave a single precipitin band against antiserum to homologous whole cells. Similar antigen preparations were purified from M1 enzyme lysate of A, viscosus SK4 and A. naeslundii ATCC 12104 cell walls. © 1982, National Institute of Infectious Diseases, Japanese Journal of Infectious Diseases Editorial Committee. All rights reserved.