Magnesium sulfate is effective in the treatment of eclampsia as well as in that of essential hypertension. It has both anticonvulsive and hypertensive properties without deleterious effects on the fetus or newborn. The present authors report here the hemodynamic data gathered after intravenous administration of the drug in two patients with eclampsia, one of whom had pulmonary edema also.Patient 1, aged 22 years, with no remarkable medical history, was in the 37th week of her first pregnancy when hypertension (190/100 mm Hg) and proteinuria (3 gm/24 hours) were diagnosed. Her weight gain was 11 kg. The abrupt occurrence of convulsions led to a cesarean section and the birth of a normal infant weighing 2250 gm. New convulsions and a massive pulmonary edema occurred after the cesarean section. Upon admission, the patient had a PaO2at 24 mm Hg and a PCO2at 45 mm Hg under an FiO2of 0.5, and her pulmonary edema was rich in protein (49 gm/liter). An optic fundus examination showed papilledema, and the cranial tomodensitometer disclosed a cerebral edema. She was placed on artificial ventilation and given thiopental.After the administration of magnesium sulfate, the patient's blood pressure was reduced to 140/80 mm Hg, and convulsions did not reappear after discontinuation of thiopental 12 hours later. A brisk diuresis (1.81) occurred between the 4th and 7th hour after magnesium sulfate administration, resulting in a negative water balance. The pulmonary edema cleared up within 24 hours, and artificial ventilation was discontinued. The brain and papillary edemas disappeared also. A renal examination, made 2 months later, yielded normal results.Patient 2, aged 24 years, with a previous rapidly progressive extracapillary glomerulonephritis, was in the 24th week of her first pregnancy when she became oliguric in spite of plasmaphoresis treatment. Eclampsia developed in the 27th week, when the patient was edematous and hypertensive (190/110 mm Hg). After magnesium sulfate administration, blood pressure decreased to 135/100 mm Hg, and the convulsions ceased. Later hypertension and uremic state were controlled by beta-blockers and daily hemodialysis, but the fetus died 4 weeks later.Hemodynamic studies were performed in both cases by means of a Swan-Ganz catheter and thermodilution techniques. Before the administration of magnesium sulfate, and at 30, 60, and 120 minutes after, measurements were taken of the following: systemic blood pressure, right auricular pressure, pulmonary artery pressure, wedge pressure, and cardiac output. Systemic and pulmonary vascular resistances were derived from these measurements, and the cumulative water balance (infusion-diuresis) was calculated.The results are summarized in Tables 1 and 2. In both patients, after magnesium sulfate administration, there was a progressive fall in blood pressure. Cardiac output decreased, but systemic vascular resistance did not change. Wedge pressure, pulmonary artery pressure, and pulmonary vascular resistance decreased. Cumulative water balance during the first 120 minutes did not change significantly (-50 ml in patient 1 and +120 ml in patient 2).