Distribution of cerebellothalamic neurons projecting to the ventral nuclei of the thalamus was examined in the cat, using the horseradish peroxidase (HRP) method. After injections of HRP within the lateral or ventrolateral portions of the ventro-anterior and ventrolateral nuclear complex of the thalamus (VA-VL), neurons labeled retrogradely with HRP were seen contralaterally in the cerebellar nuclei; many of them were situated in the nucleus interpositus anterior and nucleus interpositus posterior, and a moderate number of them were located in the nucleus lateralis. Labeled neurons in the nucleus interpositus posterior were observed mainly in the medial and ventral portions of the nucleus. On the side ipsilateral to the injections, a few labeled neurons were seen in the nucleus interpositus anterior, nucleus interpositus posterior, and nucleus lateralis. Virtually no labeled neurons were found in the nucleus medialis of the cerebellum. After HRP injections into the medial or dorsomedial portions of the VA-VL, many labeled neurons were found contralaterally in the ventral and ventrolateral portions of the nucleus interpositus posterior, as well as in the nucleus lateralis, especially in its ventral and lateral portions. On the side ipsilateral to the injections, labeled neurons in the nucleus lateralis and nucleus interpositus posterior were small in number. In the nucleus medialis only a few labeled neurons were found bilaterally in the caudal levels of the nucleus. After HRP injections centered on the ventromedial nucleus of the thalamus, many labeled neurons occurred bilaterally in the caudal portions of the nucleus madialis, with a slight contralateral preponderance, and contralaterally in the lateral and ventral portions of the nucleus lateralis. A few labeled neurons were also seen contralaterally in the ventrolateral and lateral portions of the nucleus interpositus posterior, and ipsilaterally in the nucleus lateralis.