The present report summarizes data from experiments investigating a correlation between cellular capacity to synthesize macromolecules and the extent of deoxyribonucleic acid (DNA) degradation in bacteria exposed to ionizing radiation. It is shown that a relationship exists between conditions leading to an increase in degradation and those that would be expected to inhibit the induction of a prophage. Since the organisms used were known to harbor a defective prophage, additional experiments were carried out comparing under various conditions the response to ionizing radiation of Escherichia coli 15 T- and a cured derivative. In addition, an effort was made to relate the presence of the defective prophage to colony-forming ability after irradiation. The results led to the hypothesis that the presence of the prophage results in less degradation than would otherwise be observed and may also be responsible for increased survival under certain conditions.