Polymorphonuclear leucocytes from the gingival crevice (CREV-PMN) in man have a defective capacity to phagocytose Candida albicans blastospores. Phagocytosis of zymosan particles, which detect C3b receptors, is also impaired but ingestion of latex beads coated with heat-aggregated IgG, which detects Fc receptors, is normal compared to peripheral blood polymorphonuclear leucocytes (PB-PMN). If phagocytosis is inhibited by Cytochalasin B, fewer CREV-PMN bind Candida and zymosan but the binding of IgG-coated latex beads remains unchanged. CREV-PMN have IgG (88%), IgM (45%) and C3 (48%) on their cell membrane, whilst less than 5% of PB-PMN have any of these components. Incubation of PB-PMN in fluid from the gingival crevice confers surface IgG and C3 to the cells. Such treatment also inhibits the subsequent binding of IgG coated latex beads. The results suggest that the deficiency of phagocytosis by CREV-PMN is due to decreased binding of particles to the C3b receptor of PMN, whilst the Fc receptor system remains intact.