We report that carbamazepine (Tegretol), a drug that is useful for the treatment of complex partial seizures, enhances outward, voltage-dependent K⁺ currents generated by rat neocortical cells in culture and recorded with patch-clamping techniques. This effect is seen in the presence of therapeutic concentrations of carbamazepine (10–20 μM). Furthermore, at these doses carbamazepine does not influence voltage-dependent inward Na⁺ and Ca²⁺ currents recorded in these cells. The action exerted by carbamazepine on K⁺ currents is a novel finding and might represent an important mechanism for controlling neocortical excitability and thus the generation of epileptiform activity.Key words: potassium currents, antiepileptic drugs, carbamazepine, rat neocortex.