The intestine homogenate of mice was undergone stepwise procedure of heating, centrifugation, salting out and nucleic acid isolation, and each fraction was subjected to biological activity assay using the method of crypt counting per unit intestine area in mice. The results showed that the nucleic acid extracted from intestine homogenate, either DNA or RNA, was capable of enhancing the crypt survival in mice after γ-irradiation. These are consistent with our previous results obtained by using the crude extract of intestine homogenate. Therefore, the crypt survival enhancing entities in intestine homogenate of mice are identified to be nucleic acids.