Using a standard two-stage fermentation technique, the fungus Beauveria bassiana (ATCC 7159) was found to convert the eudesmanolide vulgarin (1) to 1α,4α-dihydroxy-5αH,6,11βH-eudesman-6,12-olide (2). The use of the yeastHansenula anomala ATCC 20170 instead, produced the less polar 4α-hydroxy-1-oxo-5αH,6,11βH-eudesman-6,12-olide(3), in addition to the more polar 3α,4α-dihydroxy-1-oxo-5αH,6,11βH-eudesman-6,12-olide (4). These metabolites were characterized on the basis of their spectral data and the identity of 4 was further confirmed by chemical synthesis.