The total drug hyperthermia in the presence of metronidazole administration improves radiotherapeutic results in Pliss lymphosarcoma: tumor growth inhibition increases by 12.7-18.5%, tumor regression by 30.6-38.9%. A dose of 100 mg/kg of metronidazole combined with irradiation in the presence of moderate hyperthermia produces even a more noticeable radiosensitizing effect than a dose of 700 mg/kg without hyperthermia. A possibility of quite a high level of tumor radiosensitization with lower doses of metronidazole without toxic manifestations of the body was shown.