A urinary metabolite of rosaramicin in man was isolated and purified by a preparative HPLC method. On the basis of infrared, proton, and 13C magnetic resonance spectroscopic data, and elemental analysis, the metabolite has been identified as 20-bisureidorosaramicin. An authentic 20-bisureidorosaramicin was synthesized and shown to be identical to the urinary metabolite in infrared, 13C magnetic resonance spectral data and elemental analysis. In addition, fast atom bombardment mass spectral data of the metabolite was consistent with the structure of 20-bisureidorosaramicin. In mice receiving orally administered synthetic 20-bisureidorosaramicin, significant concentrations of rosaramicin were found in plasma, indicating the conversion of 20-bisureidorosaramicin to rosaramicin in this species.