A method has been developed to measure the levels of the growth promoter 4-hydroxy-3-nitrophenylarsonic acid (roxarsone) in samples of tissue from chickens fed on a diet supplemented with this compound. Extracts of the tissue were prepared for analysis by a trypsin enzymolysis digestion technique and bulk matrix separation was performed by anion-exchange column chromatography. Further separation of the roxarsone from other species was achieved using reversed-phase high-performance liquid chromatography. Detection of the arsenical compound was by inductively coupled plasma mass spectrometry. No roxarsone was detected in chickens fed on the supplemented diet with or without a withdrawal period (7 d on base feed after the administration period) at a quantification limit of 25 ng g-1. Recoveries for roxarsone from spiked (standard additions) samples of chicken tissue varied between 85 and 103%.