Microbial dehydrogenations of 3ft-hydroxyl groups of Digitalis cardiac aglycones by Calonectria decora and Nigrospora sphaerica were studied, both of which exhibited similar transformation pattern. Digitoxigenin was transformed exclusively into 3-dehydrodigoxigenin by C. decora and into digoxigenin and 3-dehydro-digoxigenin by N. sphaerica. Both gitoxigenin and 3-acetyl-gitoxigenin were dehydrogenated to 3-dehydrogitoxigenin. 3-Dehydro-16acetylgitoxigenin was also detected among the bioconversion products of 16-acetylgitoxigenin and 3,16-diacetylgitoxigenin by these two species.

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* Calculated by subtracting the absorption of unsaturated lactone ring at 218 mil from the U. V. of III, 1~~-{ 221 mil (log e 4.36). ** Formamide•acetone (1: 4) mixture was used as the stationary phase for these mobile phases.