The present study assessed 25 patients with unipolar major depression and 34 patients with schizophrenia along with 50 healthy, non-psychiatric controls for the presence of serum antinuclear (ANA), smooth muscle (SMA), anti-endothelial (AEA), anti-sarcolemma (ASA), thyroid gland (TGA) and parietal cell (PCA) antibodies. In the group of patients with major depression, the frequency of elevated ANA, TGA and PCA was significantly higher than in the control group. In addition, the group of patients with schizophrenia significantly more often showed increased levels of ANA and SMA than the control group of healthy volunteers. When the two psychiatric groups were compared, PCA serum titers in major depression and SMA values in schizophrenia were significantly more frequently elevated, whereas values of AEA and ASA showed no difference. These results point towards the existence of an unspecific (auto) immune disposition or reaction in at least a subgroup of patients with major depression and schizophrenia.