Two rapid and sensitive methods using visible spectrophotometry and HPLC are described for the determination of frusemide (FRU) in bulk drug and formulations. Spectrophotometry is based on a redox reaction involving FRU followed by complexation reaction and uses iron(III) and ferricyanide(III) as reagents. The resulting Prussian blue is measured at 760 urn. The HPLC determination was carried out on a reversed phase Accurasil ODS C-18 column (250 x 4.6 mm, 5 pm) using a mobile phase consisting of acetonitrile -0.1% orthophosphoric acid (pH 3) (60 + 40) at a flow rate of 1.0 mL min(-1) with UV detection at 233 urn. Working conditions of both methods have been optimized and the methods validated as per the ICH guidelines. In spectrophotometry, a regression analysis of Beer's law plot showed a good correlation in the concentration range 0.4 - 4.0 mu g mL(-1) with an apparent molar absorptivity of 4.03 x 10(4) L mol(-1) cm(-1) and a Sandell sensitivity of 7.85 ng cm(-2). The limits of detection and quantification were calculated to be 0.09 and 0.28 mu g mL(-1) respectively. The linear range of determination by HPLC was 1.01 - 121.8 mu g mL(-1). The detection limit (S/N = 3) and quantification limit (S/N = 10) were found to be 0.3 and 0.6 mu g mL(-1), respectively. Within-day accuracies and precisions were <= 3% and between-days precisions were less than 5% for all the concentrations tested. The methods were applied to the assay of FRU in tablets and injections. The label claim percentages and relative standard deviations were in the 98.28-103.24 and 0.36-2.04% range, respectively. The validity of the methods was further ascertained by parallel determination by. a reference method and by recovery studies via standard addition technique. The results showed that the procedures are suitable for routine analysis of the diuretic.