Serum immune complexes were measured in 92 patients with progressive systemic sclerosis, and elevated levels were found as follows: Raji cell assay 72% (59% after pronase treatment of Raji cell), agarose gel electrophoresis 52%, and C1q binding 24%. Forty-three (47%) had abnormal results on two or more of these tests, but only 17 (18%) had normal results by all three assays. Computer-assisted analysis of immune complex results and extensive clinical and laboratory data compiled on these patients revealed that the patients with abnormal Raji cell assays more often had diffuse scleroderma, tendon friction rubs, and positive serum antinuclear antibody tests than did patients with negative results on Raji cell assays. Individuals with immune complexes detected by C1q binding had evidence of pulmonary involvement and positive serum rheumatoid factor more frequently than did patients whose C1q tests were negative.