This paper describes a new high-pressure liquid chromatographic method used for quantitation of bumetanide in urine and plasma. Compared to previously reported methods, this assay offers the advantages of increased sensitivity, shortened sample preparation time and decreased instrumentation requirements. After addition of the 4-benzyl derivative of bumetanide as the internal standard, both urine and plasma underwent a single extraction with ethyl acetate at an acidic pH. The organic extract was separated, evaporated to dryness, reconstituted with methanol, and chromatographed using a reversed-phase C-18 radial compression cartridge with fluorescence detection. Sensitivity limits are approximately 1 ng of bumetanide per mL of plasma, with a coefficient of variation for identical samples never exceeding 6%. The method lends itself to pharmacokinetic and pharmacodynamic studies of bumetanide in humans following single therapeutic doses.