Nucleic acid hybridization studies together with a chemical cell wall analysis and physiological data indicated that some strains designated as Streptococcus sanguis II, Streptococcus sp. (“S. mitior”-S. sanguis), and “S. viridans” I, II, and IV are closely related to the type strain of S. oralis. These strains contained a directly cross-linked peptidoglycan with lysine as a diamino acid and ribitol and choline as characteristic cell wall constituents. We propose that these strains be classified as members of S. oralis. An emended description of S. oralis is given. S. oralis strains are genetically related to S. pneumoniae strains, and representatives of both species contain ribitol and choline in their cell walls.