Sera from 16 patients suffering from active psoriasis without arthropathy (2 guttate, 10 nummular, and 4 mixed type) were examined for the presence of circulating immune complexes. Five routine laboratory assay systems were used, based on C1q-binding or detection of IgG-coupled C1q and C3-breakdown products. In 14 patients, no elevated levels of circulating immune complexes were detected. One patient, who additionally suffered from late-phase HIV-1 infection, showed C1q-binding activities as well as levels of IgG-coupled C1q and C3-breakdown products in four of the assay systems, which indicated the presence of immune complexes in his serum. In another patient, with nummular psoriasis, slightly elevated levels of circulating immune complexes were measured by two of the assay systems. These results question the hypothesis of an essential pathogenic role of circulating immune complexes in psoriasis.