Increased small-intestine permeability has been documented in experimental colitis in the rat. Zinc supplementation improves mucosal repair in patients with diarrhea, as well as paracellular permeability in malnourished guinea pigs. In this study, we sought to evaluate the effect of zinc supplementation on small-and large-intestine tight junctions in rats with acute colitis. Rats were given zinc at a dosage of 2 or 30 mg/kg body wt or glucose by gavage starting 3 days before colitis was induced through the intrarectal administration of dinitro-benzene-sulfonic acid and for 7 days thereafter. We evaluated small-intestine permeability by the number of tight junctions showing extravasation of lanthanum under electron microscopy. Low-dose zinc affected none of the examined parameters of colitis severity. Rats given high-dose zinc showed colitis of similar macroscopic and biochemical severity. However, zinc-treated rats weighed more than unsupplemented ones. The number of perfused tight-junction complexes was significantly higher in animals with colitis than in controls and in the rats with colitis given high-dose zinc. Zinc may regulate tight-junction permeability, with possible implications for healing processes in inflammatory bowel diseases.