Glycine is a major inhibitory neurotransmitter in the spinal cord and in the brain stem, where it acts by activating a chloride conductance. The postsynaptic glycine receptor has been purified and contains two transmembrane subunits of 48 kDa (alpha) and 58 kDa (beta), and a peripheral membrane protein of 93 kDa. cDNA sequencing of the alpha and beta subunits has revealed a common structural organization and a strong homology between these polypeptides and the nicotinic acetylcholine and GABAA receptor proteins. The glycine receptor exhibits a heterogeneity resulting from the existence of several alpha subtypes with distinct functional properties and different developmental expressions. When present in the central nervous system in situ, as well as in primary cultures of spinal cord neurons, these receptors are localized at the postsynaptic membrane adjacent to the presynaptic release sites, thus forming functional microdomains at the neuronal surface. This distribution raises the question of the formation and the maintenance of the heterogeneity of the somato-dendritic plasma membrane.