The penicillin-induced L phase of growth of the group B, type III streptococcal strain 76-043 was examined for biochemical properties used for the identification of group B streptococci. After numerous serial subcultures in the cell wall-defective state, this stable L phase continued to produce hemolysin, hippuricase, and CAMP factor in addition to the group- and type-specific antigens. Hemolysin production by the L-phase cells was observed on solid and in liquid media containing sheep erythrocytes. Washed whole L-phase cells hydrolyzed hippuric acid. CAMP factor was detected by the characteristic hemolysis produced on blood agar by L-phase cells or filtered culture supernatants. CAMP factor activity was quantitated by an agar well diffusion system and a macrotube assay with partially purified preparations of CAMP factor and staphylococcal beta-hemolysin. Hyperimmune cow serum neutralized the CAMP activity of the L phase and parent bacterial phase to the same degree, suggesting identity of the CAMP factors. Production of hemolysin, hippuricase, and CAMP factor confirmed the bacterial origin of this L phase. Assay for these biological markers could be used to identify L-phase organisms derived from group B streptococci.