Corticotropin-releasing factor (CRF) is present in climbing fibers and their terminations on Purkinje neurons. To determine whether CRF may have a postsynaptic action in this pathway, CRF effects on the electrophysiological properties of cultured cerebellar Purkinje neurons were studied. CRF produced a dose-dependent reduction of the amplitude of the afterhyperpolarization (AHP) which follows a current-induced spike train. The effect of CRF on the AHP was specific in that CRF did not significantly alter input resistance, membrane potential, amplitude of the depolarizing-off response produced at the termination of a hyperpolarizing current pulse, or the number of depolarization-induced simple spikes. Suppression of the AHP by CRF may be one mechanism by which CRF regulates the response of Purkinje neurons to other transmitters in the climbing fiber pathway or in other inputs to Purkinje neurons.