1. The fate of bumetanide was studied in four healthy volunteers both after intravenous oral administration of [14C]-bumetanide (0.5 mg). 2. The absorption of oral [14C]-bumetanide was rapid (absorption half-life 0.61 h) and complete with a urinary recovery of about 80% of the intravenous or oral dose during 48 h. 3. The elimination of [14C]-bumetanide was rapid with a half-life of elimination (T 1/2 beta) of 1.5 h. 4. Protein bound fraction of [14C]-bumetanide in plasma was 95%. No bumetanide was found in red blood cells. 5. Four metabolites of [14C]-bumetanide were found in urine. Together they accounted for about one third of the radio-activity excreted into urine during the first 6 h after the administration of the drug. 6. Bumetanide is rapidly and completely absorbed from the gastrointestinal tract, bound extensively to plasma proteins, metabolized to some extent and excreted rapidly, principally into urine.