Cloned cDNA encoding the bovine alpha 4 subunit of the GABAA receptor has been isolated. The predicted 51 amino acid long mature protein contains an exceptionally long intracellular domain and shares 53-56% sequence similarity to the previously characterized alpha 1, alpha 2 and alpha 3 subunits. Co-expression of alpha 4 and beta 1 in Xenopus oocytes resulted in the formation of GABA-gated chloride channels with expected pharmacology, although no benzodiazepine potentiation was observed. Northern analysis indicates that a 4 kb alpha 4 mRNA is expressed in the calf cerebellum, cortex and hippocampus but is barely detectable in the rat brain.