The effects of 6-[4-(1-cyclohexyl-1H-tetrazol-5-yl)butoxy]-3, 4-dihydro-2(1H)-quinolinone (cilostazol, OPC-13013), acetylsalicylic acid (ASA) and ifenprodil on experimentally induced cerebral infarction were studied in anesthetized rabbits. Cerebral infarction was induced by injecting arachidonic acid (AA) at a dose of 0.5 mg/kg into the unilateral intracarotid artery. After the injection of AA, the brain was perfused with Indian ink, and the degree of thrombus formation was determined by calculating the percentage of perfused area in the hemispheres. The intracarotid injection of AA produced a non-perfused area amounting to 84% of the hemisphere in the injected side and 41% of the hemisphere in the non-injected side. Intravenously administered cilostazol did not produce a definite reduction in carbon-deficient area at 0.1 mg/kg, but it did produce a 49% reduction in the injected side and a 55% reduction in the entire brain at 1 mg/kg. ASA produced a 60% reduction in the carbon-deficient area in the injected side and a 62% reduction in the entire brain at 1 mg/kg. Ifenprodil at 1 mg/kg produced only a 19% reduction in the carbon-deficient area in the injected side.