Frequencies of HLA antigens (A, B, C and DR) were studied in patients with (n = 49) and without (n = 67) a family history of schizophrenia and in controls. Among the patients with a family history of schizophrenia significant increases were found in the A3 and B5 antigens while significant decreases were observed for the A1, A11 and B8 antigens. In a material of schizophrenic siblings the sharing of HLA haplotypes was consistent with normal segregation.