The HL-A typing of 90 psoriasic patients did not show any real correlation between histocompatibility antigens and psoriasic arthropathy. The study of families of 60 psoriasic patients has shown that the disease was twice as frequent among the close relatives of patients with W17 antigen. However, the HL-A typing of 4 families where several members were found to have the disease has shown that psoriasis may be transmitted independently of W17.