Over the last few years, the suggestion that HLA antigens may play a role as genetic markers in psychiatric disorders has generated considerable interest. The purpose of this study was to determine the frequency of various antigens (Ag) of loci A, B and C in schizophrenia and major affective disorders (manic-depressive psychosis). Increased frequencies were found for A3 and B5 antigens in schizophrenic disorders and for A29 and B5 antigens in manic-depressive disorders, whereas frequency of the B27 antigen was decreased in schizophrenia. These results were derived from a French caucasian population of patients selected according to DSM III criteria. However, the new antigenic specificities recenthy characterized in the HLA system were not explored in this study and final conclusions cannot as yet be drawn.