Results of an on-line HPLC-NMR analysis of human urine from a volunteer administered the anti-inflammatory drug flurbiprofen are reported. The two major human urinary metabolites, namely the glucuronides of flurbiprofen and of 4'-hydroxyflurbiprofen, have been identified using 1H- and 19F-NMR spectroscopy. In vivo conjugation of the racemic drug and its metabolites with D-glucuronic acid results in diastereomeric molecules which give resolved NMR spectra thereby permitting the diastereomeric proportions to be evaluated. The cause of the observed deviation from equal proportions is discussed. This study represents the first use of both 19F- and 600 MHz 1H-NMR spectroscopy coupled to HPLC.