The GABA receptor ρ1, ρ2, and ρ3 subunits are expressed in the retina where they form bicuculline-insensitive GABAC receptors. We used northern blot, in situ hybridization, and RT-PCR analysis to study the expression of ρ subunits in rat brains. In situ hybridization allowed us to detect ρ-subunit expression in the superficial gray layer of the superior colliculus and in the cerebellar Purkinje cells. RT-PCR experiments indicated that (a) in retina and in domains that may contain functional GABAC receptors, ρ2 and ρ1 subunits are expressed at similar levels; and (b) in domains and in tissues that are unlikely to contain GABAC receptors, ρ2 mRNA is enriched relative to ρ1 mRNA. These results suggest that both ρ1 and ρ2 subunits are necessary to form a functional GABAC receptor. The use of RT-PCR also showed that, except in the superior colliculus, ρ3 is expressed along with ρ1 and ρ2 subunits. We also raised an antibody against a peptide sequence unique to the ρ1 subunit. The use of this antibody on cerebellum revealed the rat ρ1 subunit in the soma and dendrites of Purkinje neurons. The allocation of GABAC receptor subunits to identified neurons paves the way for future electrophysiological studies.