The goal of this study was to identify GABAergic input to the cat superior colliculus from neurons located in the caudal diencephalon, mesencephalon, pons and medulla. Cells efferent to the superior colliculus were labeled retrogradely with the tracer horseradish peroxidase, and an antibody to gamma-aminobutyric acid was used to label GABAergic neurons in the same sections. The results indicate that neurons in several distinct areas of the caudal diencephalon and brainstem are both immunocytochemically labeled for GABA and retrogradely labeled with horseradish peroxidase. These areas include zona incerta, nucleus of the posterior commissure, anterior and posterior pretectal nuclei, nucleus of the optic tract, superior colliculus, cuneiform nucleus, subcuneiform area, substantia nigra pars reticulata and pars lateralis, periparabigeminal area, external nucleus of the inferior colliculus, the area ventral to the external nucleus of the inferior colliculus, mesencephalic reticular formation, dorsal and ventral nuclei of the lateral lemniscus, and the perihypoglossal nucleus. The role that such diverse inhibitory input to the superior colliculus might play, particularly in influencing eye movements, is discussed.