A sensitive and simple liquid chromatography/mass spectrometry (LC/MS) method was developed for the determination of terephthalic acid isopropylamide, the final metabolite of procarbazine in human urine. A solid-phase extraction with C 18 cartridges was used followed by LC/MS with a single mass spectrometer (SSQ 7000 from Finnigan). Terephthalic acid isobutylamide was the internal standard. The quantification limit was 30 ng/mL in urine (6 Â noise). This assay was applied for drug monitoring of terephthalic acid isopropylamide in urine after oral administration of procarbazine in children and adolescents with Hodgkin lymphomas.