[en] As soon as 2 hours after X-irradiation of white rats and mice at a dose of 700 rad and guinea-pigs at 300 rad disturbances have been observed in deamination of nitrogen compounds in mitochondrial fractions of liver and small intestine. 1500 rad irradiation of mongolian gerbils does not result in appearance of hystamine deaminase or adenylate deaminase activities. Enhancement of radioresistance of animals by either feeding them with the grasses that constitute the feed of mongolian gerbils or administering aminoehtylisothiouronium prevents the development of typical disturbances of deamination in the liver and small intestine