Six patients with systemic lupus erythematosus were treated with azathioprine in a dosage of 500mg to 100mg per day together with steroids. Four of these patients showed improvements of clinical and laboratory findings in which serum immunoglobulin and antinuclear antibody titer decreased and C′3 increased in a a few cases. Although it is difficult to evaluate the effectiveness of this immunosuppresive agent in view of clinical and laboratory findings, it is deserving of further study as an additional treatment of systemic lupus erythematosus.