BACKGROUND In our routine practice, we observed a reduced incidence of fetal acidosis (umbilical artery pH < 7.20) at cesarean delivery during spinal anesthesia when a combination of phenylephrine and ephedrine was used as first line vasopressor therapy, compared with using ephedrine alone. METHODS The study was randomized and double blind. It compared phenylephrine 100 microg/ml (phenylephrine group), ephedrine 3 mg/ml (ephedrine group), and phenylephrine 50 microg/ml combined with ephedrine 1.5 mg/ml (combination group), given by infusion, to maintain maternal systolic arterial pressure at baseline during spinal anesthesia for elective cesarean delivery. RESULTS Fetal acidosis was less frequent in the phenylephrine group (1 of 48) (P = 0.004) and less frequent in the combination group (1 of 47) (P = 0.005) than in the ephedrine group (10 of 48). The mean systolic arterial pressure was similar for the three groups: Phenylephrine group median 98% (IQR 94-103) of baseline, ephedrine group 100% (96-106) and combination group 101% (97-108) (P = 0.11). The mean heart rate was higher in the ephedrine group (median 107% [IQR 99-118] of baseline) than in the phenylephrine group (88% [82-98]) (P < 0.0001), or the combination group (96% [86-102]) (P < 0.0001). Nausea and vomiting were less frequent in the phenylephrine group (nausea 17%, vomiting 0%) than in the ephedrine group (nausea 66%, vomiting 36%) (P < 0.0001), or the combination group (nausea 55%, vomiting 18%) (P < 0.0001). CONCLUSIONS Giving phenylephrine alone by infusion at cesarean delivery was associated with a lower incidence of fetal acidosis and maternal nausea and vomiting than giving ephedrine alone. There was no advantage to combining phenylephrine and ephedrine because it increased nausea and vomiting, and it did not further improve fetal blood gas values, compared with giving phenylephrine alone.