Bacillus stearothermophilus, a thermophilic bacterium isolated from the Kuwaiti desert, produced a variety of monohydroxy androstene derivatives and an oxidized product when incubated with exogenous testosterone for 24 h at 65degreesC. The major metabolite was identified as androst-4-en-3,17-dione while minor metabolites included 6alpha-hydroxyandrost-4-en-3,17-dione, 6beta-hydroxyandrost-4-en-3,17-dione, 6alpha-hydroxytestosterone, and 6beta-hydroxytestosterone. These metabolites were purified by TLC and HPLC followed by their identification using H-1- and C-13-NMR and other spectroscopic data.