The effectiveness of the cytotoxic drug, cyclophosphamide, has been evaluated in 16 patients with refractory uveitis. Clinically significant suppression of inflammation occurred in nine of nine patients with peripheral uveitis. Results were less predictable in other forms of uveitis. Toxic side effects of cyclophosphamide were less than those reported with mercaptopurine and other metabolic inhibitors or those associated with long-term high dosage systemic steroid therapy. Combined steroid and cyclophosphamide therapy was most effective in suppressing inflammation. Cyclophosphamide decreased the risk of adverse effects of hypertension and diabetes in patients on prolonged steroid therapy. Lymphopenia with or without leukopenia correlated best with control of ocular inflammation. Cyclophosphamide is a potentially useful drug in the care of patients with significant autoallergic disease.