A total of 48 patients with juvenile chronic arthritis (JCA) were typed for HLA-A, -B, -C, -D and -DR antigens and 36 patients were also typed for HLA-D/DR associated "DR"-antigens with the primed lymphocyte typing technique. In the total group of patients, we found increased frequencies of HLA-B27, HLA-Dw/DP5 and HLA-Dw/DP8, and decreased frequencies of HLA-Dw/-DR/DP2. The increased frequencies of HLA-Dw/DP8 and the decreased frequencies of HLA-Dw/-DR/DP2 were primarily found among patients with persistent pauciarticular arthritis. The frequencies of HLA-Dw/-DR/DP4 were increased in patients with polyarticular arthritis. The frequencies of HLA-B27 and -Dw/DP5 were increased in both pauciarticular and polyarticular arthritis. The results indicate (i) that genetic factors controlled by HLA confer susceptibility and/or resistance to JCA, and (ii) that the clinical subdivision of JCA into pauciarticular and polyarticular JCA can be supported by the presence of different genetic markers (HLA-antigens) in the two groups of JCA-patients. If these data can be confirmed HLA-D, -DR or DP typing may be of value in the prognostic evaluation of patients with pauciarticular onset JCA.