Action of carbamazepine (50 mg/kg i.p.) and phenytoin (60 mg/kg i.p.) on the activity of cerebellar neurones was studied in rats under urethane anaesthesia. Carbamazepine markedly decreased the firing frequency of all ten neurones recorded continually before and after drug administration. The same conclusion was reached when a group of 53 cells recorded before drug administration was compared with 48 neurones recorded after carbamazepine administration only. The effects of phenytoin were ambiguous--a decrease as well as an increase in frequency was recorded. The solvent used did not change cerebellar unit activity. Cerebellum cannot be considered as a possible target structure for phenytoin but it might be a target for carbamazepine action.