The phenotypic characteristics of 215 strains of oral streptococci were compared on the basis of the results of sorbitol, raffinose and trehalose fermentation, ammonium from arginine production, aesculin hydrolysis, H2O2 production, susceptibility to 2 U bacitracin, and growth in 4% NaCl solution. Eleven different species were identified. Among the most noteworthy findings were the low number of H2O2-producing strains of Streptococcus sobrinus, the effective discrimination between Streptococcus sanguis and Streptococcus mitis on the basis of raffinose fermentation, and the phenotypic similarity between Streptococcus oralis and the former mutans group. To avoid the creation of new species, the term biotype is proposed to designate phenotypically distinct organisms which do not qualify as different species.