The parallel induction of sister chromatid exchange (SCE) and single-gene mutation was quantified in Chinese hamster ovary cells following exposure to nine different physical or chemical agents representing a wide variety of inducing lesions. For each agent, the frequency of induced SCE was linearly related to the induction of mutation, but the efficiency of SCE formation relative to mutation induction differed for each. Studies in repair deficient cells suggested that unrepaired lesions enhanced the induction of both SCE and mutation but that the degree of enhancement was not necessarily the same for both endpoints.