Enzyme immunoassay for the quantitative determination of CIC-C1q in human serum or plasma.Circulating immune complexes are present in many individuals with Systemic Lupus Erythematosus (SLE) and Rheumatoid Arthritis (RA), especially with any of the vasculitides complications. Levels of CICs have been reported to show correlation with disease activity in that higher levels are reported during active phases of the disease. Many tests have been developed for the detection of CICs, including PEG precipitation and radial immunodiffusion and cellular based assays such as the Raji cell assay. No single procedure appears to detect all types of CIC’s, however, those procedures which detect CIC’s containing fragments of complement (e.g. C1q and C3d) appear to detect clinically relevant events. C1q binds with greatest avidity to immune complexes ranging in size from 19 to 27 S. In serum sickness, which is the prototype immune complex disease, this size of complex has typically been found deposited in tissue leading to damage.