Binding studies suggest the presence of at least two pharmacologically distinct 'central' benzodiazepine receptors in the brain. Since central benzodiazepine receptors are allosteric modulatory sites on GABAA receptors, this evidence indirectly points to the existence of at least two GABAA receptors. Werner Sieghart describes biochemical studies that have identified several different alpha- and beta-subunits of these receptors, and molecular biological studies in which the genes encoding a variety of different alpha-, beta- and gamma-subunits have been isolated, sequenced and expressed in Xenopus oocytes. These studies all point to the existence of multiple GABAA receptors in the brain.