High regioselectivity in the microbial oxidation of C-7, C-3 and C-12 hydroxyl groups of cholic, chenodeoxycholic, deoxycholic and hyocholic acids 1-4 is reported. The tested microrganisms have been isolated from 50 enviromental samples withdrawed from an industry that extracts and purify bile acids. (C) 1998 Elsevier Science Ltd. All rights reserved.