Collagen-anticollagen immune complexes were demonstrated indirectly in RA synovial fluids by digestion with collagenase and subsequent antibody determination. Elimination of C1q was performed by affinity chromatography using an anti-C1q column. Binding of C1q to collagen-anticollagen complexes was proven by demonstrating that collagenase-caused liberation of collagen antibodies was abolished or distinctly reduced after passage through the anti-C1q column. Binding of C1q to collagen-anticollagen immune complexes was proven via the fixation of these aggregates onto the anti-C1q column. This was achieved in those 7 RA synovial fluids which contained distinctly demonstrable collagen-anticollagen complexes.