Azathioprine (1.7 to 4.3 mg/kg/day) was administered to 11 patients with nephritis of systemic lupus erythematosus (LE) (positive LE cell test). Prior therapy with prednisone was ineffective, had toxic effects, or both. Sustained improvement in nephritis (hematuria, proteinuria, serum electrolytes, edema) occurred gradually in three patients, transient improvement occurred in two, immunologic improvement occurred in only one patient and five (three uremic) patients were not improved. Four patients died during or shortly after therapy of 7 to 53 days duration. Azathioprine-induced remissions of prednisone-resistant lupus nephritis were infrequent. Some remissions did not occur until after leukopenia and systemic infection had complicated therapy.