Water and electrolyte transport were determined in rat ileum and colon using the single-pass perfusion technique. Intraperitoneal dopamine caused prompt stimulation of both ileal and colonic water absorption. The dopamine effect was mediated by both specific dopamine and alpha 2-adrenergic receptors. Haloperidol, a specific dopamine antagonist, and yohimbine, an alpha 2-adrenergic antagonist, inhibited the effect of dopamine in ileal absorption; both antagonists alone had no effect on basal water transport. Bromocriptine (intravenous and intraluminal) stimulated ileal and colonic water absorption, which was inhibited by haloperidol and yohimbine, and reversed cholera toxin-induced ileal secretion. Magnitude and time-courses of the increased water absorption in ileal loops, inoculated with saline, were the same as in loops, inoculated with saline, suggesting that bromocriptine acted to reverse cholera toxin-induced secretion by stimulating absorption. Bromocriptine had no effect on the cyclic adenosine monophosphate increase caused by cholera toxin. We conclude (a) dopamine stimulates water absorption in vivo in rat ileum and colon; (b) this dopamine effect is via specific dopamine and alpha 2-receptors; (c) bromocriptine stimulates water absorption in ileum and colon and also acts by dopamine and alpha 2-receptors; and (d) bromocriptine reverses cholera toxin-induced secretion.