Technical Abstract: Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes, including the formation of sulfated and glycosidated conjugates. A class of aromatic compounds important to the citrus industry is the furanocoumarins in grapefruit, and their metabolism in humans is critically involved in the "grapefruit/drug interactions". Thus far, the metabolism by fungi of the major furanocoumarins, including 6', 7'-epoxybergamottin (EB), 6', 7'-dihydroxybergamottin (DHB), and bergamottin (BM) has received little attention. In this study, the metabolism of EB, DHB, and BM by a number of fungi has been investigated. Of particular interest were the findings made with Aspergillus niger, which was observed to convert EB into several metabolites, DHB, bergaptol (BT), and a novel water-soluble conjugate (WSM). In addition, BM was hydrolyzed to BT, which was further metabolized to WSM. Structure of the novel WSM was identified as bergaptol-5-sulfate using mass spectrometry, UV absorption spectrum, chemical deconjugation, and 1H and 13C NMR spectroscopies, in which a sulfate group was attached to C5 of psoralen. Similarly, the fungus had a capability of metabolizing xanthotoxol, a structural isomer of BT, to a novel xanthotoxol-8-sulfate. A possible metabolic pathway by A. niger of furanocoumarin metabolism using unknown enzyme activities, such as a cleavage of a geranyl group by etherase-like enzyme and addition of a sulfate group by sulfotransferase-like enzyme, is discussed.