Eleven patients with intractable rheumatoid arthritis were treated with total lymphoid irradiation (total dose, 2000 rad) in an uncontrolled feasibility study, as an alternative to long-term therapy with cytotoxic drugs such as cyclophosphamide and azathioprine. During a follow-up period of five to 18 months after total lymphoid irradiation, there was a profound and sustained suppression of the absolute lymphocyte count and in vitro lymphocyte function, as well as an increase in the ratio of Leu-2 (suppressor/cytotoxic) to Leu-3 (helper) T cells in the blood. Persistent circulating suppressor cells of the mixed leukocyte response and of pokeweek mitogen-induced immunoglobulin secretion developed in most patients. In nine of the 11 patients, these changes in immune status were associated with relief of joint tenderness and swelling and with improvement in function scores. Maximum improvement occurred approximately six months after irradiation and continued for the remainder of the observation period. Few severe or chronic side effects were associated with the radiotherapy.