With an in vivo method, transepithelial net fluid transport and intestinal motility were recorded continuously in rat jejunal segments perfused with a modified Krebs-Henseleit solution with or without the bile salt sodium deoxycholate (4 or 8 mM). The bile salt produced a net fluid secretion and characteristic intestinal contractions. The two effects of the bile salt developed simultaneously and were quantitatively related to each other. Both effects disappeared when the bile salt was removed from the perfusate and diminished when the luminal perfusion was stopped. Hexamethonium (intravenously) and lidocaine (applied topically on the intestinal serosa) inhibited both effects, whereas indomethacin (intravenously) was ineffective. Atropine (intravenously) selectively abolished the intestinal contractions without affecting net fluid transport. Extrinsic denervation of the intestines performed 3 weeks before acute experiments did not influence the results. It is concluded that the bile salt stimulated both fluid secretion and intestinal contractions by activating a local nervous reflex mechanism consisting of a presynaptic cholinergic neuron and two postsynaptic neurons, one of which is cholinergic and innervates the intestinal smooth-muscle cell, and the other of which is noncholinergic and nonadrenergic and innervates the epithelium.