Pregnant Syrian hamsters were given 30 mg/kg ethylnitrosurea on the 15th day of pregnancy. Among 29 newborn animals, 22 could be grown up, 14 of which developed malignant tumors. Besides tumors of the trigeminal nerve which appeared first, particularly tumors of peripheral nerves were observed. In addition one nephroblastoma and one melanoma of the subcutis were induced. There were no tumors of the brain and spinal cord. The peripheral nervous tumors showed intensive regressive changes. In general, these tumors can be classified within the group of “malignant neurinomas”.