BACKGROUND: This study was designed to compare the efficacy of an ephedrine intramuscular injection with crystalloid or colloid administration for the prevention of cardiovascular change during spinal anesthesia undergoing Transurethral Resection of Prostate (TURP). METHODS: Eighty ASA I-II patients scheduled for TURP under spinal anesthesia were randomly allocated to receive non of the vasopressors or fluids (control group), 40 mg of i.m. ephedrine (ephedrine group), 15 ml/kg of i.v. lactated Ringer'solution (crystalloid group), and 8 ml/kg of i.v. pentastarch(colloid group). 12 mg of 0.5% hyperbaric tetracaine was injected through a 24 gauge Quinke needle at the L4-5 interspace in all patients. All patients were placed in the supine position and blood pressure (BP) and heart rate were recorded at 1-min intervals for 10 min, 2-min intervals for the next 10 min and subsequently at 5-min intervals. The sensory level was determined by pin prick test using 27 gauge needle. RESULTS: In the ephedrine group, systolic blood pressure was significantly greater than the other groups between 1 and 40 min after spinal anesthesia. (p<0.05) The changes in diastolic BP, mean BP and heart rate in the all groups were similar. CONCLUSION: The result of intramuscular injection of ephedrine may be more effective than crystalloid or colloid adminstration for the prophylaxis of hypotension during spinal anesthesia undergoing TURP.