The frequency of the HLA antigen DR4 has been determined in healthy individuals with serum IgM RF. HLA DR4 was found in 11.6% of these persons as compared with 27% in healthy controls. Thus, no association between IgM RF and HLA-DR4 could be found in this material of healthy individuals. HLA-DR3 was found in 35% of healthy RF-positive persons, which was no different from the 30% prevalence among healthy controls. HLA-DR3 did not seem to be associated with high immune responsiveness of RF in RF-positive individuals.