The activity of single Purkinje cells and other single neural units was recorded extracellularly from the cerebellar cortex of anesthetized cats during surface cerebellar stimulation with parameters similar to those used in human beings with epilepsy. At a stimulation rate of 0.5 Hz, most Purkinje cells responded with a simple stimulus-locked suppression of activity, although some showed more complex sequences of suppression and activation. At a stimulus rate of 10 Hz, essentially all responsive Purkinje cells showed a suppression of activity. Most of the other units responded to stimulation in the same manner. These effects were observed immediately adjacent to the stimulating electrodes and as far away as 6.5 mm. Therefore, surface stimulation of the cerebellum with parameters equivalent to those used in epileptic patients suppresses rather than activates Purkinje cells. These findings do not support the hypothesis that Purkinje cell activation accounts for seizure suppression in epileptic patients.