Loop diuretics have become indispensable in the management of patients with cardiac decompensation and severe edema. To evaluate the relative potency of these agents, bumetanide and furosemide were compared in 20 patients with edema associated with congestive heart failure in a double-blind, parallel study design. The dosage of the drugs administered daily for three days was 1 to 2 mg bumetanide or 80 mg furosemide. Both agents were highly effective in reducing the edema and relieving the symptoms of heart failure. Muscle cramps and abdominal pain as side effects were deemed not severe. Laboratory values indicative of mild hypochloremic alkalosis and hyponatremia were observed in two patients. Hypokalemia and reversible eighth-nerve involvement were not apparent in this study.