The pharmacokinetics and metabolism of orally administered bumetanide were studied in five healthy subjects and in five patients with renal insufficiency. Healthy subjects excreted 51% of the dose as unchanged drug in the urine, whilst the patients with renal insufficiency excreted only 11% of the dose as bumetanide. Similarly the urinary excretion of the gamma-hydroxybutyl metabolite was reduced from 6% in healthy subjects to 2.3% in patients with renal impairment. In both groups of subjects the mean elimination half-life of the metabolite was greater than for bumetanide. The results indicate a possible accumulation of bumetanide and metabolite in patient with renal failure.