A method is described for the recovery of purified T-antigen from crude trypsin extracts of an avirulent strain of M-1 protein deficient, T-type 1 group A Streptococcus. The purified T-antigen was resistant to enzymatic degradation with trypsin and pepsin, formed a single precipitin line with standard T-1 antiserum, failed to react with antisera for teichoic acid, group A carbohydrate, and cross-reactive protein antigens, stimulated only a single precipitin system when rabbits were immunized, contained glycine, aspartic acid, glutamic acid, lysine, and serine as the five most predominant amino acids, and consisted of subunit size isomers.