Bumetanide and furosemide were compared for efficacy in reducing edema due to congestive heart failure in 28 patients (21 receiving bumetanide and seven receiving furosemide) in a long-term study for periods from one week to 18 months. In both groups the patients showed decreases in body weight, abdominal girth, edema, hepatomegaly, blood pressure, and heart rate. Commonly observed decreases frequently achieved statistical significance, more often with bumetanide, but the differences between treatments were rarely statistically significant. Both drugs were generally well tolerated. A breast nodule and gynecomastia were each reported once in the bumetanide group as was gynecomastia in one patient who had been on furosemide, all remotely related to test drugs. Soft stools, flatulence, mild constipation, and diminished vision each reported once in the bumetanide group were judged to be unrelated or remotely related to the drug therapy. Tendencies toward hypokalemia, hypochloremia, alkalosis, and hyperuricemia without clinical gout were deemed the result of the pharmacologic action of the diuretics. Others were attributable to the underlying disease state of these patients. Both diuretics proved to be effective in the treatment of cardiac edema and other manifestations of heart failure. Bumetanide treatment beyond six months in 11 patients indicated continued safety as well as efficacy.