The effect of PGE1 and PGF2 alpha in the ischemic intestinal tract were examined. In 40 mongrel dogs, we studied ischemic models of small intestine. PGE1 or PGF2 alpha was injected into the anterior mesenteric artery after reperfusion according to each occlusion time, and the tissue blood flow was measured on both mucosal and serous sides of small intestinal loop by laser flowmeter to examine the relation to the extent of tissue damage. Tissue blood flow of the ischemic intestine after the injection of PGE1 increased by 148-208% in the 3-5 hr occlusion group and by 86-110% in the 7-10 hr occlusion group. Tissue blood flow after the injection of PGF2 alpha decreased by 39-59% in the 3-5 hr occlusion group and by 1-15% in the 7-10 hr occlusion group. These results indicate that the effect of PGE1 and PGF2 alpha in the ischemic intestine would be available up to 3-5 hr of ischemia. Histological examination revealed that viability of the remaining crypt was high in the PGE1 injection group but low in the PGF2 alpha injection group. These findings suggest that PGE1, if try at the early stage, would be effective for the treatment of ischemic lesion.