In determination (in the precipitation reaction in agar gel) of antibodies to the polysaccharide (streptococcus, group A) in the sera of patients suffering from erysipelas there were revealed antibodies against the specific determinant of polysaccharide A. An increase in antibodies in the patients with primary and repeated erysipelas was observed from the second week of the disease; in patients suffering from relapsing erysipelas their titre was increased from the first days of the disease and persisted at this level during the whole observation period (4 weeks). The majority of the patients suffering from relapsing erysipelas 4 weeks and 6 to 12 months after the relapse displayed no changes in the serum antibody level, or its slight fall was seen. The duration of persistence of antibodies to polysaccharide A in testing at the remote periods after the relapse apparently depended on slow reduction of their level and was not associated with any new infection with streptococcus, since the great percentage of the patients studied at this period were subjected to bicillin-5 therapy. The data obtained served as an additional confirmation of participation of hemolytic streptococcus of group A in the development of erysipelas.