Identification of 6 beta-hydroxydexamethasone as a major urinary metabolite of dexamethasone in man has been accomplished by nuclear magnetic resonance spectroscopy and gas chromatography-mass spectrometry. Mass fragmentographic measurements revealed that more than 30% of the intravenously or orally administered dexamethasone dose was excreted in the 24-h urine as 6 beta-hydroxydexamethasone, while only a small fraction of the dose was excreted as unchanged dexamethasone and its glucuronic acid conjugate.