Two siblings with chronic discoid lupus erythematosus and several family members were found with heterozygous C2 deficiency. An association with histocompatibility markers HLA‐B 18 and HLA‐D w2 was demonstrated, and the slow allotype of factor B was present. Linkage studies in this family suggested a close linkage between the C2 deficiency gene and genes coding for B18, Dw2, and BfS antigens. One HLA‐A CB/DBF recombinant was observed showing closer linkage between HLA‐D and Bf than between HLA‐B and Bf.