An approach to the assessment of reticuloendothelial function that quantitates clearance specifically mediated by membrane receptors for C3b and immunoglobulin (Ig)G has been applied in man. Clearance of isologous erythrocytes coated with IgM or C3b or coated with IgG were examined in patients with primary biliary cirrhosis (PBC), chronic hepatitis, or alcoholic cirrhosis and normal control subjects and compared with the clearance of aggregated human serum albumin. Clearance of these three types of particles varied independently. None of the patients studied had a defect in the clearance of aggregated albumin. No patient with PBC (0:6) had delayed clearance of IgG-coated erythrocytes; one of six patients with chronic hepatitis had delayed clearance of these cells. Indeed, four of six with PBC had increased rates of IgG-mediated clearance. In contrast, six out of six patients with PBC had an unequivocal defect in clearance mediated by C3b receptors. The patients with PBC varied widely in terms of duration of symptoms, degree of cholestasis, and histologic stage of disease. No defect of C3b-mediated erythrocyte clearance was found in the patients with chronic hepatitis or alcoholic cirrhosis. Furthermore, a patient with severe cholestasis secondary to large duct biliary obstruction exhibited normal C3b-mediated clearance. The defect in C3b-mediated clearance in PBC did not correlate with serum levels of individual complement components or inhibitors or with the presence of circulating immune complexes as measured by the Clq precipitation assay. Thus, measurements of receptor specific clearance, but not clearance of aggregated proteins, have revealed a highly specific defect in reticuloendothelial function in PBC.