This study was desinged for compare the efficacy of ephedrine infusion that of crystalloid administration in reducing the incidence of hypotension during spinal anesthesia. Sixty ASA 1 and 2 patients scheduled for transurethral prostatic resection and lower extremity surgery under spinal anesthesia were ramdomly allocated to receive either 15 ml/kg crystalloid (crystalloid group) or an ephedrine infusion (infusion group). Spinal anesthesia was performed using 12-14 mg of 0.4% tetracaine. Analgesic sensory level was T10 in both groups, Thirty patients in the crystalloid group received crystalloid solution (Ringer'lactate solution, 15 ml/kg) within 20 min prior to induction of spinal anesthesia. Thirty patients in the infusion group immediately after induction spinal anesthesia received ephedrine infusion at a rate 5 mg/ min for the first 2 min and then 1 mg/min for the next 18 min. Cardiovascular responses (systolic blood pressure and heart rate) and complications (hypotension, nausea and vomiting) after induction of spinal anesthesia were compared and results were as follows; 1) The incidence of hypotension was ll/30 (36%) in the crystalloid group and 3/30 (10%) in the infusion group (p<0.001). 2) Systolic blood pressure after induction of spinal anesthesia in the crystalloid group significantly decreased from 5 min to 20 min as compared to the infusion group (p<0.05). But, systolic blood pressure did not decrease siginificantly until 9 min after spinal anesthesia in the infusion group. 3) The mean heart rate after induction of spinal anesthesia in the crystalloid group significantly increased at 1 min as compared to infusion group; thereafter, there was no significant difference between the two groups. 4) The incidence of nausea and vomiting was 1/30 in the crystalloid group and 0/30 in the infusion group; The difference between the two groups was not significant. 5) Reactive hypertension or tachycardia did not occur in either group. Considering above results, we conclude that a prophylactic ephedrine infusion is effective for minimizing and managing hypotension associated with spinal anesthesia.