The effect of a single post-irradiation intestinal lumen dilatation injection of one of mononucleotides, nucleosides or nucleic acid bases on intestinal crypt survival after 980 cGy abdominally γ-irradiated mice has been studied. The results showed that, any one of these nucleic acid components can produce the same enhancing effect of crypt survival as that did by polymerized calf thymus DNA. This fact suggests that, the radiorestorative effect of exogenous nucleic acids on the intestinal crypt cells depends not upon the action exerted by their highly polymerised state, but rather by their various enzymatic degradation products.