Using a sensitive, specific Raji cell radioimmunoassay we have analyzed the sera of 35 patients with psoriatic arthritis (PsA) for IgA-containing circulating immune complexes. In addition, the 125I-Clq binding assay and the Raji IgG radio-immunoassay were used to measure IgG or IgM containing circulating immune complexes. Twenty-eight of thirty five (80%) patients with PsA were found to have IgA-containing circulating immune complexes. In contrast, only 13 of 35 (37%) had IgG-containing circulating immune complexes detected using the Raji IgG assay and 10 of 33 (33%) had IgG- or IgM-containing immune complexes detected using the 125I-Clq binding assay. There was no significant difference in the frequency, level, or type of immune complexes detected in any of the clinical subtypes. There was however a significant correlation between the level of IgA-containing circulating immune complexes and the severity of the arthritis as determined by linear regression analysis (p less than 0.05). The finding of IgA-containing circulating immune complexes in 80% of patients with psoriatic arthritis as well as the significantly higher levels of these complexes in the patients with more severe arthritis suggests that IgA-containing circulating immune complexes may play a role in the pathogenesis of psoriatic arthritis.