Sera from 29 colon cancer patients and 16 elderly normal controls were compared using the Raji radioimmunoassay and the Clq binding assay. By the Raji assay 11 of 29 cancer patients had evidence of circulating complexes, while by the Clq assay only 4 of the 29 patients had complexes. There was no significant difference between the levels of circulating complexes in the patient or control groups. With respect to individual patients the results obtained by the Raji assay did not correlate with those obtained by the Clq binding assay.