Five β₯-aminobutyric acid (GABA)subunits were cloned from a white perch retinal cDNA library and expressed in Xenopus oocytes. The deduced amino acid sequences indicated that all are highly homologous to the GABAsubunits cloned from mammalian retinas; two clones (perch-1A and perch-1B) were in the 1 family, two (perch-2A and perch-2B) were in the 2 family, and one clone has been tentatively identified as a perch-3 subunit. When expressed in Xenopus oocytes, all but one of the subunits (3) formed functional homooligomeric receptors. However, the receptors expressed by each of the GABAsubunits displayed unique response properties that distinguished one from the other. For example, receptors formed by perch-1B subunits were more sensitive to GABA than the receptors formed by other GABAsubunits, the dose-response curves for the various receptors revealed different Hill coefficients, and there were differences in the kinetics of the GABA-induced currents. In addition, the GABA-mediated current-voltage curve for 2 receptors was approximately linear, whereas the responses from 1 receptors showed outward rectification. A further division in the properties of the GABAsubunits was revealed in their responses to imidazole-4-acetic acid (I4AA); the drug behaved as an antagonist on A-type receptors and a partial agonist on the B-type receptors. These results suggest that there is a large diversity of GABA c receptors in the vertebrate retina, probably formed by homooligomeric and heterooligomeric combinations of GABA subunits, that exhibit different functional properties.