Cholesterol oxidase activity was studied during biotransformation of cholesterol to androsta-1,4-diene-3,17-dione (ADD) by Chryseobacterium gleum. Spent LB media, containing cholesterol (3 mMa parts per thousand 1 g l(-1)) where the bacterium was grown for 24 h, at 30A degrees C with constant shaking at 120 rpm, had the highest enzyme activity (167 U mg(-1)). The growing cells produced 0.076 g ADD from 1 g cholesterol l(-1).