BACKGROUND: A large number of bacterial, fungal and microalgal species are able to bio-transform steroid compounds. Among them, fungi from the Mucor genus have been shown to mediate hydroxylation, oxidation, and desaturation by the double bond formation and epoxidation of various steroid substances. Mucor racemocus has not been studied for its ability to modify androst-1,4-dien-3,17-dione, a pharmaceutically important steroid precursor. RESULTS: The filamentous fungus M. racemosus was applied for bioconversion of androst-1,4-dien-3,17-dione (ADD, 1) in a 5-day fermentation. Microbial metabolites were purified chromatographically and identified on the basis of their spectral data as 17 beta-hydroxyandrost-1,4-dien-3-one (II), 14 alpha-hydroxyandrost-1,4-dien-3,17-dione (III), 15 alpha-hydroxyandrost-1,4-dien-3,17-dione (IV), 15 alpha,17 beta-dihydroxyandrost-1,4-dien-3-one (V), 14 alpha,17 beta-dihydroxyandrost-1,4-dien-3-one (VI), and 6 beta,17 beta-dihydroxyandrost-1,4-dien-3-one (VII). CONCLUSION: Observed modifications included hydroxylation at C-6 beta, C-14 alpha, C-15 alpha positions and 17-carbonyl reduction. The best fermentation conditions for production of hydroxysteroid-1,4-dien-3-one derivatives were found to be 25 degrees C at 150 rpm for 5 days with a substrate concentration of 0.5 g L-1. (C) 2009 Society of Chemical Industry