Distributions of seven blood groups (ABO, MNSs, P, Rh, Duffy, Kidd and Xg) were studied in a total of 118 Japanese patients with affective disorders. The patients were diagnosed according to the DSM-III: (1) Major Depression (= Unipolar Disorder, UP) (2) Bipolar Disorder (BP) and (3) Other Affective Disorders. The following results were found: (1) a high frequency of the B blood group in all patients with affective disorders compared with controls; (2) a high frequency of the Fy(a+b+) and a low frequency of the Fy(a+b-) in all patients with affective disorders, UP and BP compared with controls; (3) a low frequency of the Jk(a+b+) and a high frequency of the Jk(a+b-) in BP compared with controls and with UP.