The effect of cold stress on lung tumours induced by 7,12-dimethylbenz[a]anthracene (DMBA) was investigated in ICR male and female mice. When mice were exposed to cold stress at 0 +/- 1 degree C for 2 h, three times per week (every other day) for 3 months, the rectal temperatures and hepatic glutathione levels were significantly decreased. On the other hand, when DMBA (10 mg/kg) was subcutaneously injected into neonatal mice, lung tumours were observed in 81.8% of non-stressed mice of both sexes 4 months after injection. However, when mice treated with the same dose of DMBA were exposed to cold stress under the same conditions, lung tumours were observed in 53.3% and 30.3% of the male and female mice 4 months after DMBA injection. In addition, although DMBA (1 mg/kg) caused lung tumours in 20% or 40% of the treated male or female mice 4 months after injection, it did not cause lung tumours in all of the male and female mice exposed to cold stress. These results suggest that cold stress may inhibit lung tumours induced by chemicals.