Immunoglobulin heavy chain (Gm) and kappa light chain (Km) allotype and phenotype frequencies were compared in 173 patients with rheumatoid arthritis (RA) and in 798 controls. No significant differences were found between allotype or phenotype frequencies in overall RA and control groups. However, the Gm(zaxfngb) phenotype and G1m(x) allotype were increased in HLA-DR4 positive RA patients compared with DR4 negative patients and controls, suggesting that immunoglobulin heavy chain genes interact with HLA in the pathogenesis of RA. All four patients with pulmonary fibrosis were Km(1) positive suggesting a possible role for immunoglobulin kappa light chain genes in the pathogenesis of pulmonary fibrosis found in rheumatoid patients.