Effects of polyphenolic compounds isolated from green tea (Camellia sinensis) on the growth and adherence of Porphyromonas gingivalis onto human buccal epithelial cells were investigated. Green tea polyphenols, especially (-)-epigallocatechin gallate (EGCg) which is a dominant component of tea polyphenols, completely inhibited the growth and adherence of P. gingivalis onto the buccal epithelial cells at concentrations of 250-500 micrograms/ml. Among the polyphenolic compounds, (-)-epicatechin gallate (ECg) and (-)-gallocatechin gallate (GCg) were effective next to EGCg in these activities. On the other hand, (+)-catechin (C(+)), (-)-epicatechin (EC), (+)-gallocatechin (GC), and (-)-epigallocatechin (EGC) had very much less activity. These results indicate that the inhibitory effect on the adherence of P. gingivalis onto the buccal epithelial cells is attributed to the presence of the galloyl moiety, which is ester-linked with the 3-OH of the catechin moiety in the polyphenolic compounds.