Ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline, EQ) is widely used in various food products and in animal feeds because of its powerful antioxidant activity. This compound was recently found to cause not only many unfavourable side-effects in animals fed with feeds containing it, but also adverse effects in people exposed to it at work. In the present study, DNA damage induced by EQ in human lymphocytes has been assessed. The alkaline single cell gel electrophoresis assay (comet assay) was used to measure DNA damage. The cells were treated for 1 h with EQ doses ranging from 1 to 250 microM in the absence or in the presence of an exogenous metabolic activation system (S9mix). The obtained results showed that EQ-induced DNA damage in human lymphocytes in a dose-dependent manner; the observed DNA fragmentation induced by EQ in the presence of metabolic activation system was always significantly lower, as compared to cells treated with the same doses of EQ alone.