The short-chain fatty acids acetate, propionate and butyrate induced a concentration-dependent increase of short-circuit current (Isc) in the rat distal small intestine in vitro. They were ineffective in the proximal small intestine. The increase of lsc in the distal small intestine was dependent on the presence of Cl- and HCO3- ions. It was blocked by the inhibitor of the Na(+)-K(+)-Cl(-) -cotransporter, bumetanide, and by the Cl- channel blocker, 5-nitro-2-(3-phenylpropylamino)-benzoate, indicating that short-chain fatty acids evoke an anion secretion. The secretion induced by propionate was blocked by the neurotoxin, tetrodotoxin, and inhibited by the muscarinic antagonists, atropine. In contrast, indomethacin, a cyclooxygenase inhibitor, or nordihydroguaiaretic acid, a lipoxygenase inhibitor, were ineffective. These results indicate that short-chain fatty acids stimulate chemosensitive neurones in the rat small intestine in a region-specific manner, which induce anion secretion by the release of mainly acetylcholine.