A sensitive, simple and rapid ulna fast liquid chromatography (UFLC)-ESI-MS/MS method was developed for the determination of 2-hydroxyflutamide in human plasma using tegafur as the internal standard The plasma sample was pretreated with methanol for protein precipitation and the analytes were separated on an Ultimate C18 column (5 mu m, 2 1 mm x 50 mm, MD, USA) with the mobile phase consisted of acetonitrile and water (2 1, v/v) Detection was performed on a triple-quack upole tandem mass spectrometer under a negative multiple reaction-monitoring mode (MRM) The mass transition ion-pan was followed as m/z 290.90-204 8 for 2-hydroxyflutamide and 198 9-128 8 for tegafur Linear calibration curves were obtained in the concentration range of 1 742-1452 ng/ml with a lower limit of quantification of 1 742 ng/ml The ultra- and inter-batch precision values were less than 8.1% and 5 6%, respectively The established method was successfully applied to a bioequivalence study of two flutamide preparations (250 mg) in 20 healthy male volunteers (C) 2010 Elseviei B.V. All rights reserved