The biotransformation of hydrocortisone (1) by Fusarium solani and Aspergillus ochraceus was investigated for the first time. After 10 days at 30 A degrees C, just one metabolite was produced by both fungi: 11 beta, 17 alpha, 20 beta, 21-tetrahydroxypregn-4-en-3-one (2) established on the basis of spectroscopic data. The reaction was reduction of the 20-carbonyl group. Time course study determined by HPLC showed 60 and 45 % yield for the metabolite by F. solani and A. ochraceus, respectively.