Summary. 726 heterozygote rats with a Yoshida-sarcoma of 8 to 9 g received in six series in the first group 60 mg kg -1 and in the second group 80 mg kg -1. In every 45 to 55 tumor-animals we used the following forms of application: 1. series intravenous, 2. series intramuscular, 3. series intraperitoneal, 4. series subcutaneous, 5. series peroral, 6. series per anum administrations, 7. series untreated tumoranimals, 8. series normal rats, 9. series normal rats for histological examinations. The tumor growth determined each second day by means of the plasticine method allowed a comparative examination of the following parameters:I. Rate of tumor regression respectively recidivation, 2. Time of complete tumor regression after beginning therapy. 3. Survival rate of the animals etc. Besides histological examinations of the intestinal tract had been carried through after intravenous, peroral and per anum administration in high doses. The evaluated parameters did not show any difference in the result due to the form of application, that means that cyclophosphamide in spite of its selective activation in certain structures can be used equivalently in all known forms without loss of effect of the cancerotoxic component, reinforcement of the by-effects respectively local injuries.Zusammen]assung. An 726 heterozygoten Ratten mit einem ¥oshida-Sarkom yon 8 bis 9 g wurden in sechs Serien in der ersten Gruppe 60 rag. kg -1 und in der zweiteu Gruppe 80 rag-kg -1 verabreicht.