Prenatal and neonatal Sprague-Dawley rats were given a diet deficient in or with an excess of Vitamin A and at the age of 55 days female progeny were treated with a single i.g. dose of 80 mg/kg DMBA or 50 mg/kg MNU. Under these experimental conditions it was found that the exposure of perinatal rats to a diet containing an excess of Vitamin A caused a decrease in the amount of DMBA- and MNU-induced DNA damage in the mammary gland and the liver of the female offspring. When diets were deficient in Vitamin A there was a dual effect in terms of DNA damage detected in the same organs, namely DMBA caused an amount of DNA damage comparable to controls, while the extent of DNA damage induced by MNU greatly increased in both organs. These results indicate that Vitamin A can permanently change the sensitivity of adult progeny to chemically induced DNA damage when it is given to pregnant and lactating females.