BACKGROUNDS: The effects of thiopental on cerebral circulation and metabolism are well known while those of propofol are not so. The present study is designed to investigate the effects of propofol on cerebral circulation and metabolism and to compare them with thiopental at equianesthetic dose. METHODS: In sixteen mongrel dogs under halothane anesthesia, baseline heart rate(HR), mean arterial pressure(MAP), intracranial pressure(ICP), cerebral perfusion pressure(CPP), cerebral blood flow(CBF), cerebral metabolic rate for oxygen(CMRO2), cerebral vascular resistance(CVR), and Ratio of CBF to CMRO2 (CBF/CMRO2) were recorded. MAP, ICP and CBF was measured at femoral artery, epidural space and posterior sagittal sinus respectively. CPP, CMRO2 and CVR was calculated. After propofol 5 mg/kg(n=8) or thiopental 10 mg/kg(n=8) was slowly injected intravenously over 1 minute, the above parameters were measured or calculated sequentially until 60 minutes. RESULTS: HR did not change after propofol injection while increased by 7.5%, 7.4% and 7.5% at 4, 5 and 6 minutes after thiopental injection. MAP decreased by 34%, 21%, 15% and 12% at 1, 2, 3 and 4 minutes after propofol injection while decreased by 10% at 1 minute after thiopental injection. ICP decreased by 40%, 39%, 42%, 47% at 1, 2, 3, and 4 minutes after propofol injection while decreased by 14%, 13% and 14% at 6, 7 and 8 minutes after thiopental injection. CPP decreased by 33% and 19% at 1 and 2 minutes after propofol injection while did not change after thiopental injection. CBF decreased by 20% at 5 minutes after propofol injection while decreased by 16% and 18% at 5 and 10 minutes after thiopental injection. CMRO2 decreased by 34%, 34%, 36% and 15% at 5, 10, 15 and 20 minutes after propofol injection while by 8% at 5 minutes after thiopental injection. CVR did not change after propofol injection while increased by 23% and 22% at 5 and 10 minutes after thiopental injection. CBF/CMRO2 did not change after injection of propofol or thiopental. CONCLUSIONS: Propofol has more potent and persistent effects on cerebral circulaion and metabolism than thiopental.