Summary—Gamma‐amino‐butyric acid (GABA) is an established inhibitory neurotransmitter in the central nervous system (CNS) and it has also been identified in the bladder. We have investigated in the rabbit the effect of GABA on detrusor activity.Rabbit detrusor muscle strips were made to contract by electrical stimulation of their autonomic nerves or by the addition of carbachol. The addition of GABA caused substantial inhibition of muscle contraction. GABA acts on 2 classes of receptors‐GABAAand GABAB. The inhibition was mediated via the GABABreceptors as its effect was mimicked by baclofen (a GABABagonist) and inhibited by 2‐hydroxysaclofen (a GABABreceptor antagonist). Inhibition was not prevented by bicuculline (a GABAAreceptor antagonist). This inhibition may be due to a direct muscle effect since the inhibition, which occurred with carbachol‐induced contraction, was not abolished by the addition of tetrodotoxin.GABA, acting via the GABABreceptor, produces substantial inhibition of muscle contraction in the rabbit uinary bladder. This raises the possibility of using GABABanalogues in the treatment of detrusor