The one-dimensional whole-cell protein patterns and a variety of biochemical characteristics of the type and reference strains of Streptococcus intestinalis and Streptococcus alactolyticus were studied. All the data revealed that strains of both species were indistinguishable. Reported differences in haemolytic activity and presence of Lancefield antigens were not reproduced. All strains were alpha-haemolytic. The S. intestinalis type strain possessed the group G antigen, but a second S. intestinalis reference strain and all of the S. alactolyticus strains possessed the group D antigen. All strains produced urease activity (albeit some after prolonged incubation), a characteristic considered important for S. intestinalis. Given the congruence between whole-cell protein electrophoresis and percentage of DNA-DNA hybridization, these data suggest that Streptococcus intestinalis Robinson et al. 1988 is a junior synonym of Streptococcus alactolyticus Farrow et al. 1984.