The diuresis induced by chlorothiazide (Diuril) was studied in 15 patients hospitalized for toxemia of pregnancy, 100 women whose pregnancies were progressing normally, except for varying degrees of pitting edema of the legs, and 35 additional patients in whom the edema, being complicated by hypertension with or without proteinuria, led to the diagnosis of toxemia of pregnancy. Doses of 500 mg., one to four times daily, resulted in striking increase in the urinary excretion of sodium and chloride ions and of water, with corresponding loss of body weight. Potassium excretion was also increased, but not so strikingly, and the excretion of ammonia and titratable acids was less significantly affected. The intravenous administration of 5 to 10 mg. of chlorothiazide per kilogram of body weight caused similar diuresis beginning within 20 minutes after the injection, without any significant effect on blood pressure and pulse rate. The data showed that chlorothiazide can be used with satisfactory results and with minimal side-effects in the treatment of edema of pregnancy.