The present multicentral clinical study performed in 6 institutes demonstrated that the novel immunosuppressive agent, 15-deoxyspergualin (DSG), is very effective on rejection. In 34 cases of rejection, 30 were treated with DSG at 40 mg/m2 (1 case), 80 mg/m2 (7 cases), 120 mg/m2 (9 cases), 180 mg/m2 (9 cases), and 220 mg/m2 (8 cases). The overall remission rate was 79% in 34 cases of rejection including accelerated, acute, and chronic rejection in different periods after transplantation. Analyzing the remission rates of early phase acute rejection occurring within 3 months after transplantation according to treatment pattern, the remission rate was 100% in 3 cases treated with DSG alone (using DSG 1 week or longer after other agents), 88% in 8 cases treated by rescue use of DSG (using DSG within 1 week after other agents), and 86% in 7 cases treated by combined use of DSG with other agents. Adverse reactions included reductions in WBC and platelets, anemia, perioral numbness, gastrointestinal troubles, and others. However all these symptoms were so mild that DSG treatment was not discontinued. Further studies are necessary on the effect of DSG, especially in acute rejection under conditions that reduce the many influences of other agents as much as possible.