BACKGROUND: Hydralazine produces cerebral vasodilation, which could appear differently according to which kind of anesthetics was used. SjO2, CBF and AJDO2 have been studied during general anesthesia with enflurane, isoflurane or propofol in 42 patients undergoing spinal surgery. METHODS: Forty-two healthy adult patients were divided into Group P (Propofol-N2O, n = 15), Group E (Enflurane-N2O, n = 15) and Group I (Isoflurane-N2O, n = 12). During the course of the study, the anesthetic concentration was constant. Induced hypotension was provided with hydralazine 20 mg in combination with a continuous infusion of esmolol within 50 - 100ng/kg/min. Arterial blood and jugular bulb blood were obtained and analyzed at normotensive and hypotensive period, respectively. SjO2, was compared within and between groups. RESULTS: SjO2 values of Group P were 66.2 +/- 7.7%, and 81.5 +/- 6.1%, those of Group E were 79.5 +/- 5.6%, and 78.9 +/- 4.9% and those of Group I were 82.0 +/- 6.2%, and 84.4 +/- 3.7% at normotension and hypotension, respectively (P < 0.05 between Group P and Group E, P < 0.05 between Group P and Group I, P < 0.05 within Group P). CONCLUSIONS: When the changes of CBF is assumed with that of SjO2, it may be concluded that CBF increased with hydralazine-induced hypotension in propofol-N2O anesthesia. It may be suggested that hydralazine reverses propofol induced cerebral vasoconstriction.