There is controversy over the subject of malnutrition as a potential risk factor for cancer; we studied the effect of chronic malnutrition on the development of tumors in rats prenatally exposed to the carcinogenic ethylnitrosourea. Twelve pregnant Wistar rats were administered on the 19th day of gestation with a single i.v. dose of 30 mg/kg of ethylnitrosourea. Immediately after weaning, at 23 days of age, half of the offspring were nourished with a protein-deficient diet (less than 6%), which consisted mostly of a corn-based diet with high calorie and low fiber contents. In the adult age, 83 rats (74%) developed a tumor of the nervous system; in comparison with controls, we found no differences in time of development, site and histological characteristics of the tumors that developed in animals subjected to chronic malnutrition.