Trichoderma hamatum KCh25 was used to study the mode of transformation of a series of 3-oxosteroids. This potential has not been previously examined. The strain promoted 1-dehydrogenation, which have been rarely observed in fungi cultures. The metabolism of cortexolone resulted in efficient conversion to 1-dehydrocortexolone, with no other product isolated. The other routes of biotransformations of the substrates included: hydroxylation at equatorial 11 alpha, 6 alpha, and 12 beta positions, ester bond hydrolysis, oxidation of 17 alpha-hydroxyl group, C-17/C-20 bond scission, and the ring D-lactonization. The correlation between a steroid compound structure and the transformation profile and also succession of the observed reactions has been noticed. (C) 2006 Elsevier Inc. All rights reserved.