The HLA antigens, A, B and DR, were studied in 141 patients with erosive, seropositive rheumatoid arthritis (RA). The frequency of the B27 antigen was significantly increased among patients with a family history of symmetrical polyarthritis compared with blood donor controls (p less than 0.001) and with patients without a family history of polyarthritis (p less than 0.005). The frequency of DR4 was significantly (p less than 0.001) increased among the RA patients, but there was no significant association between DR4 and a family history of polyarthritis.