Abecarnil, bretazenil, and Ro 19-8022 inhibited the binding of [3H]Ro 15-4513 to diazepamsensitive and -insensitive sites in the rat cerebellum and cerebral cortex, but all three had a much higher affinity for the diazepam-sensitive sites in both tissues. The GABA-shift for bretazenil and Ro 19-8022 was low ( < 2) for all sites studied, consistent with their partial agonistic profile. The GABA-shift for abecarnil was appreciably higher for diazepam-sensitive binding in the cerebellum than in the cerebral cortex (1.97 vs 1.18). Furthermore, the GABA-shift for abecarnil was markedly different for the diazepam-sensitive and -insensitive sites in the cerebellum (1.97 vs 0.71). All three compounds inhibited [3H]Ro 15-4513 binding to the diazepam-sensitive sites with a slope factor > 1, suggestive of positive cooperativity in their binding to GABAA receptors. Abecarnil only partially inhibited diazepam-insensitive binding of [3H]Ro 15-4513 in the cerebellum, indicating that this site can be differentiated into abecarnil-sensitive and -insensitive components.