Carvacrol represents a very frequent constituent of essential oils and occurs in many kinds of plants. Though human beings comequite often into close contact with this phenol derivative, its biological effects are not sufficiently known. In this paper we investigated the influence of carvacrol given to rats in drinking water on resistance of their liver and testicular DNA against the oxidative agent hydrogen peroxide H(2)O(2). Carvacrol was dissolved in tap water and given to rats either in concentrations of 30 and 60 mg/1 kg/day during 7 days or in concentrations of 15 and 30 mg/1 kg/day during 14 days. Control animals were given tap water only. After the given time the rats were sacrificed and hepatocytes and testicular cells were isolated and treated with different concentrations of H(2)O(2) (0-250 microM, 5 min, on ice). Then the level of DNA lesions was detected by single cell gel electrophoresis. The results of both types of application of carvacrol showed that DNA of cells isolated from carvacrol-treated animals was significantly more resistant to damaging effects of hydrogen peroxide than DNA of control animals. We assume that the observed DNA-protective effects of carvacrol, which was given to rats during a short time of their life, could be associated with an increase of antioxidant activity of liver and testicular cells in these animals.