A total of 907 strains of bifidobacteria isolated from the feces of breast-fed and artificial milk-fed infants were studied. Their assignment to known species of the genus Bifidobacterium was primarily based on DNA homology relationships. The strains were classified as B. bifidum, B. breve, B. catenulatum, B. dentium, B. infantis, B. longum and B. pseudocatenulatum. The distribution of these species is reported.