Abstract: Sodium camptothecin is a new anticancer drug used in this country. Recently, we have studied further its influence on immune activity in mice. The results were as follows:Two strains of transplantable mouse tumor(hepatoma & ascitic reticulosarcoma, ARS) were employed. Experiments showed that tumor-bearing mice could reject second isograft of the same tumor implantation. This phenomenon is referred to concomitant tumor immunity(GTI). Taking GTI as criteria, the immunosuppressive effect of camptothecin was investigated. It was found that the drug exhibited significant suppressive effect on GTI when injected ip 1 mg/kg for 9 consecutive days in mice. The schedule of Q4D showed moderate suppression, whereas a single injection of 40 mg/kg produced the least effect. No marked influence on immunity was found when camptothecin was injected ip 12.5 mg/kg for 2 days.Besides, the immunosuppressive effect of camptothecin was not persistant and the recovery period was about 9 days.