BACKGROUND It is known that when isobaric bupivacaine is applied for Caesarean delivery, phenylephrine is superior to ephedrine in preventing rostral spread of spinal anesthesia. In this study, we prospectively investigated whether phenylephrine can prevent rostral spread of spinal hyperbaric bupivacaine. METHODS We randomly divided 32 patients undergoing Caesarean delivery into two groups: phenylephrine group and ephedrine group. In both groups, after the spinal injection of 2.0 ml of hyperbaric 0.5% bupivacaine, we started continuous intravenous infusion of phenylephrine or ephedrine. Blood pressure and heart rate were recorded every minute. Block height of cold sensation was assessed at 5, 10 and 15 minutes after the spinal injection. We measured umbilical artery pH after birth. Data were analyzed using a statistical software package. RESULTS Block height was significantly lower with phenylephrine than with ephedrine at 10 and 15 minutes. Umbilical artery pH was significantly higher with phenylephrine than with ephedrine. Haemodynamic changes were significantly different between the two groups. There were no significant differences in age, BMI and spinal-delivery intervals. CONCLUSIONS 1. Phenylephrine prevented rostral spread of spinal hyperbaric bupivacaine. 2. Haemodynamic changes were significantly different between the two groups. 3. Umbilical artery pH was significantly higher with phenylephrine than with ephedrine.