Arsenic trioxide (AT) has a long history of use in both traditional Chinese medicine and in modern medicine in asthma therapy.Recently,Yin et al1 found that AT even at small doses reduced the airway inflammation of sensitized guinea pigs.However the mechanism underlying this is still largely unknown.Interleukin 13 (IL-13),as one of the important TH2 cytokines,plays an important role in asthma pathogenesis through promoting eosinophilic inflammation,mucus secretion and airway hyperresponsiveness.2 To further explore the molecular anti-inflammatory basis of AT,we employed Hut-78 cells,a human T cell line,with activation via CD3/CD28 receptors to mimick in vivo co-stimulation to investigate the effect of AT on IL-13 transcription.