In a previous investigation the epicortical strychninization of chronically isolated cerebellar slabs determined on the spontaneously firing of Purkinje and granule cells an excitatory effect which was thought to be mediated indirectly, as occurs in other sites in the central nervous system. In the present series of experiments, the inhibition induced on the spontaneous unit firing of isolated or non-isolated Purkinje and granule cells by electrical stimulation of the cortical cerebellar surface was submitted to the locally administered strychnine action. During the experiments directed in this way, it was essentially observed that the inhibition under investigation was of longer duration in isolated cerebellar cortex than in the intact one and that the strychninization of the slabs, both acute and chronic, was able to prevent the appearance of the tested inhibition; the strychninization of the intact cerebellar cortex was found to be ineffective. No difference was observed as far as the strychnine action on acute and chronic slabs is concerned. From the results obtained in the present study and from the considerations reported, it is concluded that at the level of the cerebellum locally applied strychnine determines excitatory effects on the Purkinje and granule cell activity by means of a depressant action on the interneurons (basket and Golgi type II cells) which cannot exert their inhibition on the Purkinje and granule cells any longer.