In an effort to determine whether treatment with lisofylline (LSF) ameliorates intestinal barrier dysfunction in rats subjected to mesenteric ischemia and reperfusion (I/R), regional mesenteric vessels were occluded for 60 min and then undamped for 60 min more. In Protocol 1, intravenous LSF (15 mg/kg bolus then 10 mg/kg/h) was administered 5 min before ischemia. In Protocol 2, LSF (same dose) was given 1 min before reperfusion. Controls received an equivalent volume of Ringer's lactate solution. Permeability was assessed by determining the mucosal-to-serosal clearance of fluorescein isothiocyanate-conjugated dextran (4 kDa) in everted ileal gut sacs incubated ex vivo. In Protocol 1, LSF treatment during ischemia ameliorated mucosal barrier dysfunction; mean ± SEM clearances for the LSF and Ringer's lactate solution groups after 60 min of ischemia were 34.4 ± 6.1 and 64 ± 7.1 nLAnin/cm2, respectively; p = .007. Clearances after reperfusion were the same in the two groups. In Protocol 2, LSF treatment just before reperfusion ameliorated barrier dysfunction measured 60 min after the restoration of blood flow; clearances for the LSF and Ringer's lactate solution groups were 23.1 ± 3.8 and 40.2 ± 4.5 nL/min/cm2, respectively; p = .012. Treatment with LSF did not affect intestinal levels of reduced glutathione or adenosine triphos-phate or the extent of histological damage to the mucosa after I/R. Nevertheless, villus height was greater in animals treated with LSF than RLS prior to ischemia in Protocol 1 (250 ± 37 and 160 ± 15 μm, respectively; p = .04) and during reperfusion in Protocol 2 (170 ± 21 and 82 ± 7 μm, respectively; p = .002). We conclude that LSF is effective in reducing both ischemia- and I/R-induced gut barrier dysfunction, possibly due to a mechanism related to preservation of villus height.