Combination of diuretics may be indicated in patients previously resistant to furosemide alone. Profound diuresis and clinical improvement may occur after the addition of metolazone to furosemide in patients with CHF. Metolazone is particularly useful because of its prolonged duration of action, lipophilicity, and effectiveness in renal failure. Extreme caution should be exercised with this approach as massive diuresis and electrolyte disturbances may ensue.