NEW ORAL DIURETIC BRITISH those patients who have not responded to other diuretics. Summary A new diuretic drug, ethacrynic acid (MK-595), has been compared with hydrochlorothiazide in normal volunteers and oedematous patients. Structurally the two drugs are not related. Ethacrynic acid is a potent diuretic causing an excretion pattern similar to that caused by hydrochlorothiazide. It produced in oedematous patients a greater diuresis than hydrochlorothiazide, each at a dose of 50 mg. thrice daily, but the potassium loss was correspondingly greater. One patient who was resistant to hydrochlorothiazide had an adequate diuresis with ethacrynic acid. Acute gout was induced by ethacrynic acid in one patient; no other side-effects were noted. We are indebted to Dr. K. C. Mezey, of Merck Sharp and Dohme, Research Laboratories, Rahway, New Jersey, for supplies of MK-595 and for an investigational grant-in-aid. The Auckland Medical Research Foundation provided financial support for a biochemist. We wish to express our thanks to Mr.