We evaluated a 3-year-old female patient with leukocytosis, recurrent infections, severe periodontal disease, and a history of delayed separation of the umbilical stump. This patient's polymorphonuclear leukocytes (PMNs) had normal membrane depolarization responses, normal oxygen metabolism, normal granule secretion responses, normal bactericidal activity, and normal C3b rosetting. However, by fluorescent cell analysis and C3bi rosetting, it was determined that her cells lacked the C3bi receptor. In addition, the patient's PMNs showed markedly abnormal chemotaxis, adherence, and aggregation responses, and partial abnormalities were detected in PMN spreading and phagocytosis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the subject's neutrophil cytoplasts were missing a 180,000-dalton moiety. Her monocytes also had defective chemotaxis and failed to adhere and grow normally in culture. Epstein-Barr virus- transformed B cells from the patient lacked an aggregation response to phorbol myristate acetate. Laboratory and clinical evaluations of this patient's mother showed no abnormalities. These studies demonstrate that C3bi receptor deficiency can be associated with functional abnormalities in multiple myeloid cells and that the absence of C3bi receptor is associated with abnormal adherence-related functions of these cells.