The heterogeneous bacterial group known as oral streptococci was screened for the presence of cellular polyglycerolphosphate-containing lipoteichoic acid. This compound was detected in phenol extracts of lyophilized cells by an immunoassay in which polyglycerolphosphate-specific monoclonal antibody was used. Polyglycerolphosphate-containing lipoteichoic acid occurred in all 86 strains of oral streptococci examined except the Streptococcus mitis and Streptococcus oralis strains. This confirms the findings of Rosan (B. Rosan, Science 201:918–920, 1978) and Hamada et al. (S. Hamada, J. Mizuno, S. Kotani, and M. Torii, FEMS Microbiol. Lett. 8:93–96, 1980), is consistent with the results of the taxonomic study of oral streptococci performed by Kilian et al. (M. Kilian, L. Mikkelsen, and J. Henrichsen, Int. J. Syst. Bacteriol. 39:471–484, 1989), who emended the descriptions of Streptococcus sanguis, S. oralis, and S. mitis, and reflects the phylogenetic relationship among S. mitis, S. oralis, and Streptococcus pneumoniae.