The effects of the oxygenase inhibitors, 1-aminobenzotriazole (ABT), ketoconazole, metyrapone and proadifen, on the metabolism of 18 beta -glycyrrhetinic acid (18 beta -GRA) in Sphingomonas paucimobilis strain G5 were investigated. Strain G5 transformed 18 beta -GRA into a major new metabolite (M-D) in the presence of 1 mM ABT or metyrapone. M-D was purified and identified as 3 beta -hydroxy-11-oxo-olean-12-en-24,30-dioic acid by NMR and MS. Based on the structure of M-D, we propose the metabolic pathway of 18 beta -GRA in strain G5.