Lactobacillus helveticus, grown at 37A degrees C in MRS medium supplemented with 3 mM cholesterol, assimilated all the cholesterol in 42 h having 68 U mg(-1) of intracellular cholesterol oxidase activity. The strain transformed 1 g cholesterol to 0.05 g of androsta-1, 4-diene-3, 17-dione and 0.04 g of androst-4-ene-3, 17 dione within 48 h at 37A degrees C with extracellular cholesterol oxidase activity at 12 U mg(-1) and intracellular oxidase at 0.5 U mg(-1).