To compare the effect of IV magnesium with other antihypertensives in emergency department (ED) patients with hypertension. ED patients with a systolic BP>135 mmHg or diastolic BP>85 were approached for entry into the study. Those granting consent were randomly placed into one of three treatment groups: (1) 1.5 gm IV MgSO 4 (n=42), (2) a parenteral or oral antihypertensive agent (n=41), (3) both IV MgSO 4 and an antihypertensive agent (n=44). Systolic and diastolic blood pressures were measured at entry into the study and at 15, 30, 45, and 60 min after magnesium or other antihypertensive medications were given. The main outcome measure was blood pressure at 60 min, and results were compared using one-way analysis of variance with the post hoc Tukey HSD test. Compared to systolic and diastolic blood pressures at time 0, both were lower at 15, 30, 45, and 60 min in all groups (p<0.05). No significant difference in systolic or diastolic BP at any time point was observed when response to treatment was compared between the three groups. Intravenous MgSO 4 is as effective as antihypertensives at lowering BP in emergency department patients. © 2008 Humana Press Inc.