The frequency of HLA-A, B and C antigen in 53 patients and HLA-DR, DQ and Dn antigen in 31 patients of Behçet's disease was studied. All patients were Chinese, and diagnosis was made according to the Japanese Research Committee on Behçet's disease. A significantly increased incidence of HLA-B51 (P less than 0.001) and a significantly decreased incidence of HLA-B16 (P less than 0.01) was found. No significant difference was found in HLA-DR, DQ and DN antigens.