Furosemide kinetics were studied in normal volunteers and patients with renal failure. Comparison of results from intravenous bolus and intravenous infusion in normal subjects showed no significant model dependency of estimations of furosemide clearance, although the average clearance by fitting to a one-compartment model was 16% higher than that obtained by fitting to a two-compartment model. Normal subjects had a total body clearance of furosemide of 1.53 +/- 0.11 (SE) ml/min/kg, a volume of the central compartment of 2.61 +/- 0.37 L, a volume of the peripheral compartment of 2.48 +/- 0.24 L, and a half-life of 0.8 +/- 0.06 hr and they absorbed 68.9% +/- 7.1% of a solution of furosemide given by mouth. The corresponding values in patients with renal failure were 0.27 +/- 0.03 ml/min/kg, 8.02 +/- 0.96 L, 14.1 +/- 3.57 L, 14.2 +/- 2.30 hr, and 43.4% +/- 8.0%, all differing significantly different from the normal. The bioavailability of 500-mg tablets of furosemide in the renal failure patients was 43.4% +/- 7.4%, equivalent to the absorption of the dose given to the same patients in the form of a solution.