We studied the role of neutrophils in lung injury after intestinal ischemia and reperfusion (I/R) in anesthetized dogs with lung lymph fistulae. One group was subjected to 2.5 hours of balloon occlusion of the superior mesenteric artery without laparotomy, followed by 3 hours of reperfusion (I/R group, n = 7). The other group was subjected to the same procedures, except for intestinal I/R (sham operation group, n = 6). In the sham operation group, lung fluid balance, hemodynamics, extravascular water volume (Qw 1: ml/g BFDW), myeloperoxidase activity in the lung (MPO: unit/g DW), H2O2 production by neutrophils in blood (mean DCF/cell), and migration of neutrophils into the lung lymphatic system did not significantly change. In the I/R group, both lung lymph flow (Jv) and protein clearance (Qp) increased more than 2.5 fold as compared with the baseline values, while capillary pressure (Ppc) and the ratio of lymph to plasma protein concentration (CL/Cp) remained almost the same as the baseline values. Qw1 also moderately increased. MPO activity, H2O2 production, and migration of neutrophils into the lung lymphatic system increased after I/R, and were more remarkable than in the sham operation group. These results suggest that activation and migration of primed neutrophils contributes to lung injury after intestinal ischemia and reperfusion.