The time course of recovery in UV- or gamma-irradiated wild-type Schizosaccharomyces pombe has been determined by fractionated dose experiments and by measuring the rate at which the "resistant shoulder" of the survival curve was regained during post-irradiation incubation in growth medium. The kinetics of recovery after UV-irradiation were different from those after gamma-irradiation, and may be described as due to a fasy gamm-repair and a relatively slow UV-repair process. In fractionated dose experiments, for single exposures which gave about 10% survival, gamma-repair was rapid (t1/2 congruent to 2 h), began immediately, and was essentially complete within 3 h. UV-repair, in contrast, showed a lag of about 5h and was relatively show (t1/2 congruent to 10h). The nature of the recovery response was analyzed from the survival curves at intermediate times; recovery was evident as the reappearance of a shoulder. A heterogenous recovery was evident after UV-irradiation; after a 5 h lag, a progressively increasing fraction of the survivors regained UV-resistance, which suggested that some critical event or rate-limiting step was involved. A requirement for post-irradiation protein synthesis for activity of a recombinational repair pathway on UV-damage may be a factor in the UV-recovery lag. A homogeneous recovery response, however, was observed in gamma-irradiaged cells.