Responses of separate regions of rat cerebellar cortex (Cb) to inferior olive (IO) stimulation occur with the same latency in spite of large differences in climbing fiber (CF) lengths (Sugihara et al., 1993). Here, the olivocerebellar path of turtle was studied because its Cb is an unfoliated sheet on which measurements of latency and CF length can be made directly across its entire surface in vitro. During extracellular DC recordings at a given Cb position below the molecular layer, IO stimulation evoked a large negative field potential with a half-width duration of ~6.5 ms. On this response were smaller oscillations similar to complex spikes. The stimulating electrode was moved to map the IO and the CF path from the brainstem to the Cb. The contralateral brainstem region that evoked these responses was tightly circumscribed within the medulla, lateral and deep to the obex. This response remained when the brainstem was bathed in solutions that blocked synaptic transmission. The Cb response to IO stimulation had a peak latency of ~10 ms that was not dependent on the position of the recording electrode across the entire Cb's 8 mm rostrocaudal length. However, for a constant Cb recording position, moving the stimulation across the midline to the ipsilateral brainstem, and then along the lateral wall of the fourth ventricle toward the peduncle did shorten the response latency. Therefore, a synchronous Cb response to CF stimulation appears due to changes in its conduction velocity within the entire cerebellar cortex but not within the brainstem.