Effects of 3-isobutyryl-2-isopropylpyrazolo[1,5-a]pyridine (KC-404) on cerebral circulation and metabolism were examined measuring cerebral oxygen and carbon dioxide tension (BrPO2, BrPCO2) and mean arterial blood pressure (MABP) in cats. KC-404 (100 micrograms/kg) infused into the carotid artery produced no significant changes in BrPO2, BrPCO2 and MABP. 300 micrograms/kg of KC-404 infused into the femoral vein produced significant decrease in MABP, whereas BrPO2 remained constant. It is suggested that a large dose of KC-404 causes preferential cerebral vasodilation and maintenance of constant blood flow despite marked reduction in MABP.