The protective effect of NAD, FAD, ATP and p-benzoquinone administered singly or in combination to rats, was studied. The first three compounds were well tolerated (up to 640 mg/Kg body weight). However, p-benzoquinone showed a high toxicity, so it was not considered for in vivo experiments. Animals were irradiated in a137Cs gamma source (0.8 Gy/min) and the lethal dose (LD(50/30)) was 7.7 Gy.