Phenylephrine is the drug presently recommended for prevention of maternal hypotension during caesarean section. The optimal infusion dose is still undetermined. We tried to determine the optimal infusion dose of phenylephrine to prevent maternal hypotension. After Institutional Ethical committee approval, consenting one hundred ASA physical status I or II parturients for elective caesarean delivery were included randomized into 4 groups of 25 each by picking lots. Group P25, P50, P75 and P100 received phenylephrine infusion in concentrations of 25, 50, 75 and 100µg/ min respectively. After administering spinal anaesthesia a infusion was started as per group allocation. 20% change in baseline mean blood pressure was taken for intervention. Hypotension was treated with 50µg phenylephrine bolus, bradycardia treated with atropine 0.6 mg. Hypertension treated by stopping the infusion. Neonatal Apgar at 1 and 5 minutes and base deficit in cord blood was assessed. Demographic, anaesthetic and surgical characteristics were comparable. 25% of patients in group P25 had hypotension requiring bolus phenylephrine dose. 40% in group P75 and 55% in group P100 had hypertension requiring infusion to be stopped. 6 patients in group P75 and 9 patients in group P100 required atropine to treat bradycardia. Neonatal outcome were comparable in 4 groups. Conclusions: Phenylephrine in an infusion dose of 50µg/min gives stable haemodynamics with good neonatal outcome.