Seventeen patients with mild to moderate essential hypertension and controlled with antihypertensive drugs were treated with xipamid (40 mg) or hydrochlorothiazide (50 mg) in a double-blind cross-over randomized trial design. After a run-in-period of 2 weeks with placebo, all of them received either of the two drugs. Placebo treatment for 2 weeks decreased both supine as well as standing blood pressure, but it was not statistically significant. Xipamid produced a somewhat greater decrease in blood pressure than hydrochlorothiazide, but the difference was not statistically significant. Similar results were obtained in 12 newly diagnosed cases of mild to moderate essential hypertension treated with xipamid (80 mg) or hydrochlorothiazide (100 mg) daily as single drug treatment in a randomized, double-blind parallel design trial. The side effects produced by both drugs were only mild in nature. No significant changes were produced in serum electrolytes, uric acid and fasting blood glucose in this short term study with either of the drugs.