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BACKGROUND Spinal anaesthesia is the most popular and elegant approach for obstetric patients undergoing caesarean section due to its several advantages. Hypotension resulting from sympathectomy due to subarachnoid block can have detrimental effects on the foetus as well as the mother, so needs to be prevented and treated adequately. Vasopressors for the treatment of hypotension have a well-established role as vasodilatation is the primary cause of the reduction in arterial blood pressure. The primary objective of the study was to compare mephentermine and phenylephrine with respect to their clinical efficacy in maintaining arterial blood pressure during spinal anaesthesia in caesarean section and the secondary objective was to determine any untoward effects of the study drugs on the mother and foetus. METHODS This prospective, randomized, comparative, double-blind study was conducted among  90 pregnant women of ASA-I physical status having singleton pregnancies in the age group of 18-30 years undergoing elective as well as emergency caesarean section and were randomly allocated in to two groups. Group M (n=45), received 6 mg of mephenterine as an intravenous bolus (volume made up to 1 ml) and Group P (n=45), received 100 g of phenylephrine as intravenous bolus (volume made up to 1 ml) whenever hypotension occurred after spinal anaesthesia. A comparison of the mean values among the two groups was done using a student t-test. To compare more than two variables, ANOVA test was used. The p-values of less than 0.05 were considered statistically significant. RESULTS The systolic blood pressure, diastolic blood pressure and mean arterial pressure remained significantly high (P < 0.05) in the phenylephrine group as compared to the mephentermine group. The phenylephrine group also showed a significant fall (P < 0.05) in heart rate as compared to the mephentermine group. CONCLUSIONS Both the drugs were effective in treating the hypotension caused by spinal anaesthesia without any adverse effects on the mother as well as on neonatal outcome but phenylephrine had a quicker onset, better maintenance of blood pressure and can be preferred in patients in whom tachycardia is undesirable.