The therapeutic effect of prednisone combined with azathioprine was studied in 28 patients with rheumatoid vasculitis. Nine patients with severe systemic vasculitis were treated initially with 60 mg of prednisone and 2 mg/kg of body weight of azathioprine daily. Clinical signs of vasculitis decreased in all patients. Nineteen patients with only cutaneous vasculitis entered a randomized controlled study comparing prednisone plus azathioprine treatment vs continuation of various conventional antirheumatic drugs. Although measures of both vasculitis and arthritis activity improved to a greater degree in the patients treated with prednisone plus azathioprine in the first 3 months of therapy, no significant differences between the results of the two treatments were observed at the end of the follow-up period. Prednisone plus azathioprine treatment was associated with a low incidence of relapse of vasculitis, few serious complications, and a relatively low mortality. We conclude that the combination of prednisone and azathioprine is effective in the treatment of severe systemic rheumatoid vasculitis; rheumatoid vasculitis with only cutaneous manifestations has a relatively good prognosis, and there is probably no indication for therapy specifically directed at the vasculitic process.