A double-blind study of patients with essential hypertension was performed in order to determine which dosage of spironolactone (25 mg, 100 mg, or 200 mg daily), with or without hydrochlorothiazide, had the optimum hypotensive effect. The data were analyzed by two different statistical methods, in each of which multivariate analysis of variance was used. Both methods led to the conclusion that the most efficacious treatment regimen tested was spironolactone at a daily dosage of 100 mg, without hydrochlorothiazide.