Furosemide was administered intravenously to 5 healthy volunteers and 15 patients with various degrees of renal failure. Two patients were given the drug orally, The plasma half-life offurosemide averaged 0.79 hr in the healthy subjects, Although most patients with kidney disease had a prolonged half-life (t½), up 10 24.58 hr, some with advanced renalfailure had an almost normal t½. The plasma clearance of furosemide, which in the normal subjects averaged 194 ml/min, decreased proportionally with decreasing creatinine clearance, as did the renal clearance, which in the healthy subjects averaged 95 ml/min. There was no correlation between kidney function and the apparent volume of distribution or of non renal clearance. One patient was given 35S-labeled furosemide intravenously. Although the furosemide plasma t½ was essentially normal, the elimination rate of metabolites was decreased. Unlike that of healthy subjects, the main route of excretion of label was in the feces.