γ-Aminobutyric acid (GABA) is a well known inhibitory neurotransmitter in the mammalian central nervous system. GABA may be a neurotransmitter in the vertebrate peripheral nervous system, evidence has accumulated demostrating the presence of GABA receptors in the gastrointestinal tract. GABA and its metabolic enzymes (GAD and GABA-T) are present in the myenteric plexus of the enteric nervous system. High affinity GABA uptake in the plexus has been shown by release studies and autoradiography of labelled GABAergic neurons. Both GABA(A) and GABA(B) receptor sites on plexus neurons have been established pharmacologically. GABA affects the motility of intestinal preparations mainly by altering the release of acethycholine from intrinsic cholinergic neurons; stimulation of bicuculline sensitive GABA(A) receptors may increase acethycholine output whereas bicuculline insensitive GABA(B) receptor stimulation may inhibit acethycholine release. This results are consistent with a significant role played by on intrinsic GABAergic neurons in the enteric nervous system.