The intramuscular administration of RNase A (0.35–7 μ g/kg) orDNase I (0.02–2.3 mg/kg) resulted in a considerable decrease in the metastasis numberinto the lungs of animals with Lewis lung carcinoma and a decrease of the hepatic index ofanimals with hepatoma 1A. The gene discussed is RNASE1; the disease is hepatocellular carcinoma.