Hypothermia was used early in the treatment of malignant tumors. New evidence shows that hypothermia protects normal tissues from the toxic effects of radiation and chemotherapeutic drugs. Hypothermia in oncological research is calculated to increase the therapeutic ratio by protecting normal tissue while retaining the antineoplastic effect. Animal results indicate that removal of the primary tumor using cryosurgery diminishes metastatic tumor growth more than does surgical excision.