Despite some similarities, L-streptococci could be clearly differentiated from A-streptococci. Formamide, autoclaved and nitrous acid extracts of all L-streptococcal cultures studied reacted only with their specific antisera and did not cross-react with any other group specific streptococcal antigens. All 33 L-streptococcal cultures, in contrast to A-streptococci, produced beta-D-glucuronidase and beta-D-galactosidase, hydrolyzed Na-hippurate, grew on 10% and 40% bile blood agar and were agglutinated by the lectin of Arachis hypogaea. Some differences between A- and L-streptococci were also observed in their sensitivity patterns to bacitracin and sulfamethoxazole-trimethoprim.