Weanling Wistar rats of both sexes were given epichlorohydrin by gastric intubation for 2 years, 5 times a week at dosages of 0, 2, and 10 mg/kg body weight. Mortality and body weight gain were recorded and histopathological examination for tumours was carried out; after 1 year also haematology was performed. Towards the end of the study a slight dose-related increase in mortality was observed in males, along with a decrease in mean body weight in the survivors. At pathological examination a high incidence (100% for females, 81% for males) of squamous cell carcinomas of low-grade malignancy was observed in the forestomach of animals at risk (greater than 18 months) from the 10 mg/kg group. In the 2 mg/kg group forestomach tumours were found at a lower incidence (7% for females, 14% for males), whereas this tumour was not found in control animals. Other tumours diagnosed in this study occurred at background level and were not influenced by treatment.