The relationship between the presence of the DR4 antigen and other HLA antigens and in vitro production of IgM-rheumatoid factor by lymphocytes from a group of healthy young subjects was examined. Pokeweed and Epstein-Barr virus-stimulated lymphocyte cultures were examined for the production of rheumatoid factor and immunoglobulins. No significant correlation was found between the presence of the DR4 antigen and in vitro production of IgM rheumatoid factor. The presence of the B18 antigen seemed to identify a population of nonresponders when stimulated with PWM. © 1983.