Carbamazepine serum levels have been determined by gas-liquid chromatography in 24 children and 26 adults with epilepsy on chronic carbamazepine treatment. A significant correlation has been found between carbamazepine steady-state levels and doses per kilogram body weight in both children (p less than 0.01) and adults (p less than 0.05). This relationship is characterized by a significant decline in the level/dose ratio with the doses for adults (p less than 0.001) and, to a lesser extent, for children (p less than 0.05). These results are consistent with a dose-dependent bioavailability.