The amino acid glycine is an established inhibitory neurotransmitter in the spinal cord and brain stem. Its postsynaptic receptor has been purified, and cDNAs of the receptor subunits have been cloned and sequenced. Recent molecular studies indicate considerable diversity of the inhibitory glycine receptor (GlyR); this diversity stems from both the existence of several alpha-subunit genes encoding isoforms of distinct pharmacology, and alternative splicing of their primary transcripts. In situ hybridization studies reveal a widespread expression of GlyRs throughout the mammalian CNS, suggesting that glycinergic neurotransmission may be implicated in many higher brain functions.