The prevalence and possible prognostic significance of HLA-DR antigens have been studied in 129 patients with seropositive (RF-positive) classical rheumatoid arthritis (RA). HLA-DR4 was increased in RA, whilst HLA-DR2 was decreased, though it was not associated with either low titres of RF or with good prognosis. HLA-DR3-positive patients had the highest prevalence of antibodies to nuclear antigens, and the antigen correlated negatively to the presence of subcutaneous nodules, bony erosions and familial RA. RA patients possessing DR3 thus had some of the characteristics of SLE. HLA-DR5 was not present in male RA patients. An absence of familial RA was observed among DRw8-positive patients.