A fast and reliable gas chromatographic-mass spectrometric (GC-MS) method for the identification and determination of the loop diuretic torasemide in human urine is described. The usefulness of different derivatization procedures and reagents was studied. Flash methylation using trimethylanilinium hydroxide was the most convenient and appropriate procedure. The optimal urine isolation method comprised alkaline liquid-liquid extraction with ethyl acetate. After evaporation of the organic layer to dryness, the solid residue was reconstituted in the derivatizing reagent and was directly injected into the GC-MS system. Samples were analysed in the multiple ion detection mode using electron impact ionization. No interferences from other urinary compounds were found. Torasemide gave rise to a derivative that was identified by GC with Fourier transform infrared detection. There was a 70 +/- 5% recovery of torasemide. The coefficient of variation was 5% at a concentration of 0.05 microgram/ml. The method was used for the determination of torasemide in urine samples obtained from a healthy volunteer that had received a single, 10 mg dose of torasemide.