Abstract The receptor for GABA (γ-aminobutyric acid), an inhibitory neurotransmitter in the brain, has been classified into GABA A and GABA B types. The GABA A receptor was purified by means of affinity column chromatography using benzodiazepine as an immobilized ligand. The results indicated that the GABA A receptor consists of several subunits and forms a GABA-gated Cl − channel, which is coupled with the benzodiazepine receptor. The molecular weight of the GABA A receptor complex was estimated to be approximately 300 kDa. Furthermore, cDNA cloning of GABA A receptor subunits was performed and the primary structure of these subunits was deduced. The results suggested that these subunits possess four transmembrane domains in their structure which are important for the formation of the Cl − channel. On the other hand, activation of GABA B receptors induced the inhibition of adenylyl cyclase activity and phosphatidylinositol turnover via inhibitory GTP-binding proteins such as G i and/or G o. The GABA B receptor was purified using baclofen affinity and immunoaffinity column chromatographies. It was confirmed that the purified GABA B receptor protein is about 80 kDa in its molecular weight. This protein is capable of inducing the inhibition of adenylyl cyclase when it is reconstituted with G i/G o protein in the phospholipid vesicle system. Currently available data indicate that GABA A and GABA B receptors in the central nervous system are distinct not only in terms of their molecules but also their signal transduction systems. However, the primary structure and synaptic localization of GABA B receptor molecules in the brain remain to be clarified.