Soybean extract residue (scum), a waste of soybean oil production, was examined as a raw material for C-17-ketosteroid production. As a model process, its bioconversion to 9alpha-hydroxyandrost-4-ene-3,17-dione (9-OH-AD) by Mycobacterium sp VKM Ac-1817D was studied. The content of transformable sterols (sitosterol, stigmasterol and campesterol) in scum was estimated at similar to14%. The bioconversion of scum to 9-OH-AD was characterized by a long lag-period (300-350 h) followed by 9-OH-AD accumulation. The microbial or chemical elimination of fatty non-identified components resulted in sterol-enriched scum preparations. Effective conversion of these preparations by Mycobacterium sp was demonstrated: 9-OH-AD molar yield similar to65% was reached at 60h from the scum preparation containing 10g dm(-3) transformable sterols. The process productivity was comparable with that for high quality-sitosterol of wood origin (tall-oil sitosterol). (C) 2004 Society of Chemical Industry.