AbstractThe sensitivity of bacterial species to the lethal effects of radiations and alkylating agents is related to the base composition of their DNA; high guanine and cytosine (GC) content confers increased sensitivity to X rays and mustards and increased resistance to ultraviolet. Preliminary results suggest that differences in average GC content of different markers inBacillus subtilisDNA may be detectable by radiosensitivity analysis. Purine starvation, thymine starvation, or incubation with certain purine and pyrimidine analogues may alter bacterial radiation responsiveness, as reflected in changes in the slope and/or shoulder of dose‐survival curves; the responses differ characteristically with respect to such parameters as time of onset, reversibility, relative expression with X rays versus ultraviolet, oxygen‐dependence, and glycerol‐dependence. Available evidence pertaining to the molecular mechanisms of these radiosensitization phenomena is rev