The hypotensive and diuretic properties of chlorothiazide were evaluated and compared with acetazolamide in 144 pregnant women with hypertension, edema, albuminuria, or other manifestations of toxemia. Chlorothiazide was given alone in 85 patients, alternately with acetazolamide in 43, and simultaneously with acetazolamide in 16. The average effective dose was found to be 1 Gm. per day by mouth. It caused an excellent diuresis, with reduction of edema, weight, blood pressure, and albuminuria. The reduction in arterial pressure after administration of chlorothiazide was greater than that after acetazolamide. The diuresis and blood pressure reduction after chlorothiazide and acetazolamide given simultaneously was greater than that after either drug alone. The lack of the development of drug resistance and absence of significant toxicity make chlorothiazide a valuable drug for the prevention and treatment of the toxemias of pregnancy.