A panel of three immune complex (IC) assays was used in this study to test sera from patients with glomerulonephritis (GN): the Raji cell radioimmune assay (IRCA), the radio-labeled C1q binding assay (IC1qBA), and the microcomplement consumption test (MCT). The sensitivity and specificity of each assay was evaluated in preliminary studies, and the greater sensitivity (5 to 10microgram of aggreagated human gamma-globulin (AHG) per ml of serum) and IgG specificity of the IRCA was apparent. Problems related to the preliminary heat inactivation of test sera, the interaction of C1q with substances other than IC, and the effects of suboptimal storage of test sera were experienced with the MCT and, to a lesser extent the IC1qBA. The individual reactivities of the different assays were exploited by using them in combination. Thus ICs were detected by one or more of the assays in 87% of patients with systemic lupus erythematosus (SLE), 65% of patients with GN associated with other systemic diseases, and 39% of patients with primary GN. ICs were detected more frequently in patients with acute GN than chronic GN, and in patients with low serum C3, C4, and properdin factor B (C3PA) levels.