The phagocytic ingestion of clinical isolates and reference strains of Bacteroides buccae, Bacteroides oris, Porphyromonas gingivalis and Fusobacterium nucleatum by polymorphonuclear leukocytes (PMNs) was studied. Special attention was focused on the hydrophobicity of the strains. B. buccae strains, less or equally hydrophobic than PMNs, were poorly ingested without opsonization. Hydrophobic, but not hydrophilic, strains of B. oris and both hydrophilic and hydrophobic P. gingivalis and F. nucleatum strains were readily ingested without opsonization. Hydrophobicity thus contributes to the adherence of bacteria to PMNs in some, but not all, species tested. Normal human serum enhanced the ingestion of B VSports手机版. buccae, but failed to do so after heat-inactivation. Heat-inactivation of the immune serum to B. buccae strain ES57 did not reduce opsonic activity suggesting that specific antibodies enhanced the ingestion of B. buccae. .