There is experimental evidence for an axon reflex control of alkaline secretion in the rat duodenum. We have investigated if there is also an intramural reflex control of alkaline secretion similar to that demonstrated with regard to the control of the fluid transport in the rat jejunum. Alkaline secretion in the duodenum of an anesthetized rat was continuously monitored using an in situ titration technique. The segment was extrinsically denervated. Exposing the duodenal segment to 80 microg cholera toxin markedly increased alkaline secretion. This response was abolished by hexamethonium (28 micromol (10 mg) kg(-1) body wt), a nicotinic receptor blocker, lidocaine (0.5 mL of a 1% solution on the serosal surface), a local anaesthetic, and nifedipine (5.75 micromol (2 mg) kg(-1) body wt i.v.), a calcium channel blocker. The response to cholera toxin was partially abolished by granisetron (0.11 micromol (40 microg) kg(-1) body wt i.v.), a 5-HT3 receptor blocker. Atropine (1.7 micromol (0.5 mg) kg(-1) body wt i.v.), a muscarinic receptor blocker, had no effect. We therefore conclude that the alkaline secretion in the rat jejunum evoked by cholera toxin exhibits the same pharmacological properties as the fluid secretion caused by the toxin in the jejunum. This suggests that the alkaline secretion in the rat duodenum is controlled not only by an axon reflex but also by an intramural secretory reflex similar to that controlling fluid transport in the rat jejunum.