1,3-Butadiene is produced in large quantities for use in the manufacture of synthetic rubber. It is also an environmental pollutant. There is concern about exposure to 1,3-butadiene as it has been shown to produce tumours in rats, mice and an increased risk of leukaemia in humans. It has also been shown to produce germ cell effects in mice. Differences in responses to 1,3-butadiene have been reported in rats and mice, possibly due to different metabolic capabilities. The present study thus investigated somatic and germ cell effects of 1,3-butadiene in mice and its metabolites in both rats and mice to help determine species differences using different endpoints for genotoxic effects. These included DNA strand breakage as measured in the single cell gel electrophoresis (Comet assay) in bone marrow and testicular cells, and micronuclei in bone marrow cells using both the acridine orange and Giemsa staining methods. Unscheduled DNA synthesis (UDS) was also measured in the testes of mice. CD-1 mice were exposed to 1,3-butadiene by inhalation for 6 h/day for 4 weeks, and CD-1 mice and Sprague-Dawley rats to the metabolites after i.p. injection. 1,3-Butadiene did not affect liver, bone marrow and testicular cells in mice as measured in the Comet assay. After treatment with 1,2-epoxybutene in the Comet assay, there was a response in the testes in mice but not in rats and there was little or no effect in the bone marrow assay in mice but there was in rats. After treatment with 1,2,3,4-diepoxybutane in the Comet assay in mice, there was a response in the bone marrow cells but not in the testicular cells, and in rats there was also a response only in bone marrow cells. There was an increase in micronuclei in both rats and mice with both metabolites, but clastogenicity was stronger with 1,2,3,4-diepoxybutane, occurring at lower doses, than with 1,2-epoxybutene. In the UDS assay in the testes of mice, there was an increase in response with 1,2,3,4-diepoxybutane treatment but not with 1,2-epoxybutene. These studies would appear to confirm a species difference of CD-1 mice and Sprague-Dawley rats, where mice were sensitive at lower doses than rats.