BACKGROUND: Marcaine is a recently introduced hyperbaric bupivacaine. The aim of this study was to compare the difference in hemodynamic change and sensory or motor block between 0.5% hyperbaric bupivacaine and 0.5% hyperbaric tetracaine in spinal anesthesia. METHODS: Thirty patients belonging to ASA classes I and II were divided into either a tetracaine (Group I) or bupivacaine (Group II). All patients received an infusion of lactated Ringer's solution (1,000 ml). We standardized techniques and injected equal doses (12 mg) in equal volume (2.4 ml) intrathecally for spinal anesthesia. After intrathecal injection of the agents, we measured the blood pressure, heart rate, change of sensory block level according to pinprick test and motor block by the modified Bromage score until fixation was achived. RESULTS: The onset time of sensory block was more rapid in Group I than in Group II. There was no difference in the level of sensory block between Group I and Group II. The time for maximum motor block was significantly shorter in Group I than in Group II (p < 0.05). The change in systolic and mean blood pressure in Group II was less than the change in Group I. CONCLUSIONS: Bupivacaine has a longer sensory block duration, a weaker intensity and shorter duration of motor block and yields less change in blood pressure than tetracaine in spinal anesthesia. Therefore, we concluded that spinal anesthesia with hyperbaric bupivacaine may be used more safely in comparision with hyperbaric tetracaine in hemodynamically troublesome cases.