The voltage-dependency of the responses of Purkinje cells to excitatory amino acids was examined in rat cerebellar slices, using intrasomatic recordings with the single electrode voltage-clamp. In standard perfusion medium, the depolarizations evoked in these neurones by ionophoretic pulse applications (less than 300 ms) of L-glutamate, L-aspartate and quisqualate in their dendritic fields had underlying inward currents which did not increase or even decreased, as the holding potential was shifted to values more negative than -65 mV. This 'abnormal' voltage-dependency was still present in Mg2+ -free solution but was abolished in the presence of CsCl2 (10 mM) in the perfusion medium. When TTX (5 microM) and CdCl2 (0.1 mM) were further added to the bath in order to block regenerative conductances, thus broadening the range of the clamp voltages to more positive values than -50 mV, the current-voltage relation between -80 and 0 mV for responses to L-glutamate and L-asparate was almost linear. Our results support the view that low doses of both amino acids act on Purkinje cells essentially via the activation of receptors which are not of the N-methyl-D-aspartate type.