Chronic ethanol treatment which produced intoxication and physical dependence in rats, produced an increase in the specific binding of ethanol antagonist [3H]RO15-4513 in rat brain cerebral cortex and cerebellum, but not in hippocampus and striatum. The increase in both the regions was due to an increase in the number (Bmax) of receptor sites. These results suggest that the RO15-4513 binding sites on the oligomeric GABA receptor complex are altered following chronic ethanol administration, and support the notion of a unique role of RO15-4513 as an ethanol antagonist.