The effect of diabetes induced by pretreatment with streptozotocin 6 weeks prior to the study on the responses induced by gamma-aminobutyric acid (GABA), the GABA(A) agonist 3-aminopropane sulfonic acid (3-APS), and acetylcholine in the rat isolated ileum was evaluated. GABA, 3-APS, and acetylcholine showed a rightward shift in their concentration-dependent effects in the ileum that also attained a lower maximum in streptozotocin-diabetic rats as compared with control rats (p < 0.05). It is suggested that the reduced contractile responses of ileal smooth muscle to GABA and 3-APS might be due to a direct effect of diabetes on the GABAergic system or to its effect on the cholinergic system.