To investigate a possible peroral route of infective endocarditis (IE), the occurrence of staphylococci in the oral cavity was examined using saliva and supragingival plaque specimens from 56 systemically and periodontally healthy adults aged 22-43 years old (27.1+/-5.3). Nine Staphylococcus species and 334 isolates were identified. In saliva, the total occurrence rate was 83.9 % and the total number of bacteria was 10(2)-10(4) c.f.u. ml(-1). Staphylococcus aureus was the most frequent species (46.4 %), followed by Staphylococcus epidermidis (41.1 %) and others (Staphylococcus hominis, Staphylococcus warneri, Staphylococcus intermedius, Staphylococcus capitis, Staphylococcus haemolyticus, Staphylococcus lugdunensis and Staphylococcus gallinarum, isolation frequencies ranging in order from 12.5 to 1.8 %). A similar isolation tendency was observed in supragingival plaque, with a total occurrence rate of 73.2 % and amounts of bacteria ranging from 10(2) to 10(5) c.f.u. g(-1). Four common Staphylococcus species (S. aureus, S. epidermidis, S. lugdunensis and S. hominis) were isolated from nasal swab samples taken from the oral staphylococci-positive subjects. Genotyping of all 18 combinations of oral- and nasal-derived isolates by PFGE indicated that identical clones or close relatives were commonly distributed in these two cavities. Since the provision of micro-organisms from the nasal cavity was shown and occurrence rates in the oral cavity were adequate, these results suggest a possible peroral route of staphylococcal IE, as in cases of viridans streptococcal IE.