The effect of a new prostacyclin analogue OP-41483 on ischemic colonic anastomosis was investigated in dogs. Colonic ischemia was produced by devascularization of the marginal vessels in the left colon and graded into three degrees by measuring colonic blood flow with a hydrogen gas clearance method. The agent was administered intravenously after devascularization using a continuous infusion pump. The parameters studied were colonic blood flow in the submucosal layer, rate of anastomotic leakage, beta-glucuronidase activity and protein content of the colonic mucosa, and histologic changes. After administration of the agent, blood flow increased significantly and beta-glucuronidase activity at the anastomotic site was well preserved at a relatively high level in spite of ischemic change. The anastomotic leakage rate was significantly decreased. The present study proved that administration of this new prostacyclin analogue minimizes ischemic damage, and may be of considerable importance in ischemic colonic anastomoses.