The oral streptococci have undergone considerable taxonomic revision in recent years but there is still little information concerning associations between the newly defined species and disease. This study examined the identities of 47 strains of oral streptococci collected from 42 confirmed cases of infective endocarditis. By means of recently described physiological schemes, the most common species identified were Streptococcus sanguis sensu stricto (31.9%), S. oralis (29.8%) and S. gordonii (12.7%). Other related species including S. mitis and "S. parasanguis" were less common. This indicates that attention should be focused on S. sanguis sensu stricto and S. oralis when considering possible pathogenic mechanisms involved in viridans streptococcal endocarditis.