To investigate the mutagenic effects of antiepileptic drugs (AED), 39 epileptic children treated by long-term monotherapy (10 cases with Pb, 11 with Cbz, 9 with Vpa, 8 with Pht) have been studied. The long-term administration was monitored by measurement of AED serum concentrations by gaschromatography. Metaphase chromosome observations were performed using short time culture of peripheral blood lymphocytes and 100 mitoses from each proband were analyzed. A significant increase of CA in the group of patients with Pb (0.23), Cbz (0.19), Vpa (0.25), Pht (0.18) as compared with those of nine epileptic children without treatment (0.08) has been found. Because unrepaired damage of DNA may act as a possible carcinogenic potential, the shortest possible duration of AED treatment is recommended.