The role of K⁺ channels in the mediation of the nitric oxide(NO)-induced proabsorptive effect in intestinal fluid transport was investigated in a functional study, using a model of ligated jejunal loops of anaesthetized rats in vivo. The K⁺ channel opener cromakalim and the K⁺ channel blocker glibenclamide were administered under basal conditions as well as under conditions, when fluid secretion was influenced by N^ω-nitro-l-arginine methyl ester (l-NAME), prostaglandin E₂, Escherichia coli heat stable enterotoxin a (E. coli STa) or l-arginine. Intravenous infusion of cromakalim (63.5 μg/kg per min) significantly enhanced net fluid absorption compared to controls, totally abolished net fluid secretion induced by l-NAME (0.55 mg/kg per min), reversed net fluid secretion induced by intraluminal instillation of E. coli STa (10 units/ml) to absorption, but did not influence fluid secretion elicited by close i.a. infusion of prostaglandin E₂ (79 ng/min). Close i.a. infusion of glibenclamide (0.16 mg/kg per min) reversed net fluid absorption to net secretion, blocked the absorptive effect of l-arginine (8.88 mg/kg per min) and reduced the proabsorptive effect of cromakalim. The secretory effect of l-NAME was not further enhanced by glibenclamide. These results suggest that modulation of basolateral K⁺ channels by NO is involved in the mediation of its proabsorptive effect, since opening and closure of K⁺ channels mimicked, respectively counteracted, the action of NO-donors and inhibitors of NO-synthesis on intestinal fluid transport. The role of prostaglandins in the proabsorptive effect of NO remains to be elucidated. These results furthermore support the role of K⁺ channel openers as potential new antidiarrheal drugs.