We evaluated the efficacy and safety of tacrolimus in patients receiving glucocorticoid therapy for lupus nephritis. Patients with persistent nephritis were randomized to receive 28 weeks of double-blind treatment with tacrolimus (3 mg/day) or placebo. The primary endpoint was the change in the lupus nephritis disease activity index (LNDAI) calculated from scores for daily urinary protein excretion, urinary red cells, serum creatinine, anti-double-stranded DNA antibody, and serum complement. Statistical analysis was performed using the full analysis set. The LNDAI was decreased by 32.9 +/- 31.0% (mean +/- SD) in the tacrolimus group (n = 28) and was increased by 2.3 +/- 38.2% in the placebo group (n = 35) at final evaluation. There was significant improvement in the tacrolimus group. Daily urinary protein excretion showed a significant decrease in the tacrolimus group (p < 0.001). The complement (C3) level showed a significant increase in the tacrolimus group (p = 0.001). Treatment-related adverse events occurred in 92.9% of the tacrolimus group and 80.0% of the placebo group, but the difference was not significant. In patients on glucocorticoid therapy for lupus nephritis, addition of tacrolimus to basal therapy achieved significant improvement compared with placebo. Tacrolimus may therefore be a useful alternative treatment for lupus nephritis.