Logarithmic and stationary phase cultures of the wild type and a number of radiation-sensitive mutants of Schizosaccharomyces pombe were uv-irradiated and their survival curves as well as postirradiation division delay were studied. The mutants could be classified into two groups. One group showed a marked difference in the level of resistance as well as in the shape of survival curves due to a change in growth phase, while in the other group this difference was negligible. This differential response was found to to be related to a variation in uv-induced division delay in the mutants in different phases of growth. The implication of division delay on cell survival and shapes of survival curves is discussed in relation to a recently proposed model of cellular inactivation.