To compare the percentages of pregnant women with preeclampsia who reached the therapeutic serum magnesium levels between those who received maintenance magnesium sulfate infusion of 2 g/hour versus I g/hour Sixty women diagnosed of preeclampsia and magnesium sulfate that were considered for seizure prophylaxis were randomized into two groups. A loading dose of 5 g magnesium sulfate was given intravenously over 20 minutes to both groups. Maintenance doses of magnesium sulfate of 2 g/hour and 1 g/hour were given to the study and control groups, respectively. The maintenance dose was continued until 24 hours postpartum. Blood samples for serum magnesium were collected at 0, 1/2, 2, and 4 hours after the loading dose and at 2 and 12 hours after delivery. Clinical signs of magnesium toxicity were carefully monitored. Maternal and neonatal outcome were evaluated. Significantly more women in the present study group reached the therapeutic level of serum magnesium at 2 hours (70% vs. 23%, p = 0.001) and at 4 hours (80% vs. 17%, p = 0.00) after the loading dose and at 2 hours (60% vs. 20%, p = 0.003) and at 12 hours (80% vs. 37%, p = 0.001) after delivery. No clinical magnesium toxicity was observed There were no significant differences in maternal and neonatal outcomes between the two groups. The maintenance dose of magnesium sulfate at 2 g/hour was more likely to attain the therapeutic level of serum magnesium when compared to 1 g/hour with no detectable difference in maternal and neonatal outcomes.