Antibodies against recombinant 52 kD-Ro, recombinant 60 kD-Ro and recombinant La protein were determined by ELISA in over 300 central European patients with systemic lupus erythematosus (SLE). A strong association with HLA-DR3 was found for antibodies against 52 kD-Ro and La, but not for recombinant 60 kD-Ro antibodies in the absence of antibodies against 52 kD-Ro or La. Ro/La negative SLE patients still showed an increased frequency of HLA-DR3 as compared to healthy controls. These results indicated that the preferential formation of Ro and La antibodies was not due to an unspecific stimulatory effect of HLA-DR3 but that the antibody response to certain defined proteins (52 kD-Ro and La) was influenced by MHC genes in SLE. Furthermore, the association of SLE with HLA-DR3 was independent of the effects of DR3 on the formation of 52 kD-Ro and La antibodies.