Sister chromatid exchange (SCE) frequency, a sensitive indicator in mutagenicity testing, and mitotic index (MI) have been studied to observe genotoxic effects in epileptic patients on routine combinations of anticonvulsant therapy. All patients, both male and female and from various age groups, revealed an increased frequency of SCE per metaphase and a low MI (P less than 0.001) with respect to controls. A nonsignificant decrease in SCE frequency has been observed with an increase in the age of onset of epilepsy. Although the SCE frequency increased and the MI decreased in some groups with respect to the duration of epilepsy, there was no difference observed in SCE frequency with the duration of therapy.