Cellular fatty-acid profiles were obtained for streptococci of Lancefield groups A, B, C, D, N and O, and Streptococcus salivarius. The major fatty acids above isomyristate had the retention characteristics of n-myristate, myristoleate, n-palmitate, palmitoleate, anteisostearate, n-stearate, and oleate (or cis-vaccenate). Profiles were quantitatively and qualitatively similar. Strains could be identified as members of a particular Lancefield group by computer analysis with the Bravais–Pearson coefficient of linear correlation being used as a measure of association of strain pairs, since strains of the different Lancefield groups examined had distinct fatty-acid profiles.