This prospective, randomized, study was designed to compare the effect of two different preloading volumes of Ringer's lactate for prevention of maternal hypotension induced by spinal anaesthesia for Caesarean section. Eighty ASA I or II obstetric patients were randomized to two groups. Group 1 (n = 40) received 20 ml/kg of Ringer's lactate and Group 2 (n = 40) 10 ml/kg of Ringer's lactate over 20 minutes before spinal anaesthesia. The lowest mean arterial pressure (MAP) for both groups were recorded at 15 minutes after giving spinal anaesthesia, This difference in the drop of MAP from base-line at 15 minutes (mean decrease of 12.5 mmHg from baseline), between preloading with 10 ml/kg and 20 ml/kg of Ringer's was statistically significant. Twelve patients from Group 1 required bolus doses of ephedrine and 15% of these needed additional crystalloid whereas two patients from Group 2 needed ephedrine boluses and 22% of these required additional crystalloid. The difference in frequency of requirement for treatment of hypotension was not statistically significant. There were five patients in Group 1 and six patients in Group 2 who experienced nausea and vomiting, the frequency of occurrence did not show any statistically significant difference between the two groups. In conclusion, for prevention of hypotension during spinal anaesthesia for Caesarean section, infusing 20 ml/kg or 10 ml/kg of Ringer's Lactate gave similar results and we do not recommend the use of a larger volume of crystalloid for preloading before spinal anaesthesia.