In 48 patients with schizophrenia and 32 patients with affective disorders, different immune parameters were tested. Compared to blood-donors, IgG and IgM serum concentrations were increased in both the schizophrenic and affective disorders. However, these abnormalities did not differ from hospital control populations. The patients failed to show an association of antibodies considered to be characteristic of autoimmune diseases. In addition, no increased incidence of circulating immune complexes was detected. The only substantial serologic abnormality found was an elevation of C4 levels in patients with bipolar psychosis.