Group A streptococci (Streptococcus pyogenes) of several different serological types were grown in fluoresceinlabeled homologous type or group-specific globulins, thereby labeling the antigen-containing cell walls. Specific precipitation or inhibition of the labeled antibody, followed by continued incubation and examination at intervals by ultraviolet, phase, and dark-field microscopy, showed that new cell wall was then nonfluorescent. These nonfluorescent portions were differentiated by a reverse technique of culture in unlabeled globulin, followed by antibody precipitation, further growth, and fluorescent-antibody staining. This technique of differential labeling of cell wall has permitted following, for the first time in a living system, the fate of cell wall formed at different times. The results suggest that cell wall synthesis in actively growing cultures usually occurs simultaneously at at least two sites per coccus, each site representing stages in successive divisions, and that cell wall growth in Streptococcus pyogenes is not by diffuse intercalation with old wall, but is initiated at and extends both peripherally and centripetally from the coccal equator.