To study the biotransformation of phytosterol and phytosterol-containing rice germ and wheat germ ethanolic extracts to produce 4-androstene-3,17-dione (AD) and 1,4-androstadiene-3,17-dione (ADD) by Mycobacterium sp. DSM 2966 using phytosterol to hydroxypropyl-beta-cyclodextrin (2:1, 1:1 and 1:2 mol/mol) and 2 % (w/v) Tween 80 as solubilizing agents. A maximum yield of 180 +/- A 27 mg AD l(-1) and 31 +/- A 11.4 mg ADD l(-1) with a total conversion of 65 % (day 12) was obtained using 1 g phytosterol l(-1) and hydroxypropyl-beta-cyclodextrin (2aEuroS:aEuroS1 mol/mol) with 2 % (w/v) Tween 80 in the fermentation medium. The most appropriate conditions for rice germ extract and wheat germ extract which gave the maximum conversion of 22 and 43 % (day 14) were obtained by using 2 % (w/v) Tween 80. Phytosterol and wheat germ are effective sources for AD and ADD production while rice germ required further development. Hydroxypropyl-beta-cyclodextrin (2aEuroS:1 mol/mol) and/or 2 % (w/v) Tween 80 in the biotransformation process could improve AD and ADD yields, depending on substrates and biotransformation conditions.