Abstract: There is disclosed a method of protecting animals including humans against ionizing radiation by injecting the animals with a polymer having the approximate formula H(OCH.sub.2 CH.sub.2).sub.n OH, where n varies between 4 and 13. Particularly, it is found that polyethylene glycol (molecular weight between 200 and 600), polyethyleneglycolmonoethylether (molecular weight between 200 and 600), and polyvinylpyrrolidone (molecular weight up to 10,000) when injected into standard experimental animals, such as mice, protects them from the lethal effect of ionizing radiation.