A pH-stat technique was used to investigate the effects of cholera toxin (CT) on alkaline secretion from denervated intestines (jejunum, ileum, colon) in anaesthetized rats. Transepithelial potential difference (PD) was also followed in some experiments. CT, given intraluminally, caused a marked increase in jejunal alkaline secretion, whereas only a small effect was observed in the ileum and no apparent effect was noted in the proximal colon. The pronounced increase in jejunal alkaline secretion was found to be inhibited by 10-25% by hexamethonium (10 mg kg-1 body wt i.v.) and similarly by serosal application of lidocaine, whereas atropine (0.25 mg kg-1 body wt i.v.) had no effect. Thus the cholera toxin-induced alkaline secretion in the jejunum is attributed mainly to a non-nervous mechanism. The small effect of CT on ileal alkaline secretion observed in this study contrasts with the high ileal bicarbonate concentration reported in cholera by authors who estimated the concentration from the total carbon dioxide/bicarbonate contents. This discrepancy may be explained by a CT-evoked increased transport of the coupled Na+/H+ and Cl-/HCO3- exchangers, which cannot be measured with the pH-stat technique used in this study.