The implication of neutrophils-derived oxygen radicals in the formation of ischemia-reinfusion (I-R) injury in the rat stomach was evaluated. Male SD rats were subjected to 20 min hypotension and 20 min reinfusion of shed blood as we described previously (Gastroenterology 88: 1162, 1985). The area of gross gastric lesions was measured and scores of histologic damage assessed by our criteria as reported previously (Gastroenterology 94:1135, 1988). Luminol-dependent chemiluminescence (CL) was assessed in blood samples withdrawn from the portal vein and abdominal aorta immediately before killing rats. In a study prior to the I-R experiment, 3 ml of anti-neutrophils monoclonal antibody (ANA) given i.p. was confirmed to significantly reduce the number of neutrophils in blood from the carotid artery with the reduction rate being constant by 6 to 18 hr after. On the basis of this results, rats were administered ANA i.p. at the same dose 12 hr before I-R. Controls received normal rat serum. The area of gross gastric lesions in the corpus (69 vs. 191 mm2), but not in the antrum (13 vs. 20 mm3), was significantly reduced in the ANA group compared to that in control. The scores of histologic damage was significantly smaller in both the corpus (1.2 vs. 2.0) and antrum (0.8 vs. 1.5) in the ANA group than in the control. ANA significantly reduced the number of neutrophils and the CL levels in blood from both the portal vein (number, 107 vs. 915; CL, 26 vs. 235 RLU) and abdominal aorta (number, 52 vs. 368; CL, 24 vs. 268 RLU) in the ANA groups as compared to controls.(ABSTRACT TRUNCATED AT 250 WORDS)