Surmmary Three hundred and sixty-seven strains of pioneer streptococci isolated from the mouths of 40 healthy, full-term infants during the first month of life were examined by two taxonomic schemes that incorporated biochemical and physiological characteristics, IgA1 protease production and glycosidase activities. Streptococcus mitis biovar 1 and S. oralis comprised 55.0% of the pioneer streptococci isolated from neonates. S. salivarius constituted 25.3% of the isolates, while S. anginosus, S. mitis biovar 2, S. sanguis and S. gordonii accounted collectively for 11.4%. Difficulties in identifying streptococci were encountered and 8.4% of the 367 isolates could not be assigned to a recognised species.