To determine whether or not nerves lying in the lamina propria and submucosa affect ion transport by the human intestine, we studied the effects of electrical field stimulation on ion transport across the isolated ileum stripped of muscularis propria. Electrical field stimulation increased transmural electrical potential difference and the short-circuit current, and by increasing the serosal to mucosal movement of chloride (J_sm^Cl), reduced the absorption of Cl (J_net^Cl). The movement of sodium and the residual ion movement (J_net^R) were not affected. The neurotoxin, tetrodotoxin prevented all of the changes caused by electrical field stimulation, but did not prevent the responses to aminophylline, implying that tetrodotoxin affected electrically excitable cells rather than epithelial cells. Aminophylline increased the potential difference and shortcircuit current, reduced tissue conductance (G), and eliminated chloride absorption. In tissues treated with tetrodotoxin, aminophylline also reduced J_ms^Na, J_net^Na, and J_net^R; while increasing J_sm^Cl, it augmented the reduction in J_ms^Cl and caused chloride secretion. Atropine reduced baseline short-circuit current and reduced the short-circuit current response to electrical field stimulation. It was concluded that acetylcholine and other chemical transmitters that affect ion transport are released in the submucosa or lamina propria of the human ileum. The identity of the noncholinergic transmitters and the sequence of events leading to their liberation remain to be determined.