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Strains of enterococci obtained from the American Type Culture Collection and the Centers for Disease Control were examined for deoxyribonucleic acid homology by using the S1 nuclease technique. The strains studied segregated into four homology groups. All five Streptococcus faecium strains were included in a single homology group (group III), and both Streptococcus faecalis strains were included in a separate homology group (group IV). Of eight “Streptococcus durans” strains, six fell into one homology group (group I), and two fell into a second homology group (group II). The four homology groups were easily distinguished phenotypically. All eight “S. durans” strains were inactive on mannitol, sorbitol, and arabinose. Group I strains clotted litmus milk but did not form acid from sucrose. Group II strains did not clot litmus milk but formed acid from sucrose. These results are consistent with a classification scheme in which “S. durans” is a separate species. We propose that the strains included in homology group I be designated Streptococcus durans sp. nov. and that strain ATCC 19432 be the type strain of this species. The two strains in homology group II may represent a new species, but the data supporting such a proposal are presently insufficient.