We determined 27 histocompatibility antigens of A, B, and C locus with a standard lymphocyte cytotoxicity test in 125 patients suffering from primary affective disorders, 77 of bipolar type, 24 of unipolar type, and 24 with schizo-affective psychosis. Comparison with a normal control group showed significant increases in the frequencies of antigens Bw40 and Cw4 in unipolar patients and a significantly decreased frequency of antigen Cw3 in bipolar patients. The statistical significances which were at the 5% level, disappeared when the P values were corrected for the number of antigens investigated. Our results failed to confirm previous findings of significantly altered antigen frequencies among patients with primary affective disorders.