Biotransformation of 1-benzoylindole (BI) by the strains Aspergillus flavus VKM F-1024 and Aspergillus oryzae VKM F-44 was studied. The major metabolites isolated were identified as 4-hydroxyindole (4-HI), 5-hydroxyindole (5-HI), 4-hydroxy- -benzoylindole, 4-hydroxy-1-(4'-hydroxy)-benzoylindole and indole. The structure of the metabolites was determined by mass spectrometry and proton nuclear magnetic resonance spectroscopy. The pathways of BI metabolism via initial monohydroxylation at C-4 and C-5 followed by cleavage of the benzoyl substituent to yield 4-HI and 5-HI were proposed. Indole was formed as a by-product, and its role as a potent inhibitor of BI hydroxylation at C-4 and C-5 is discussed.