Technical Abstract: Fungi metabolize polycyclic aromatic hydrocarbons by a number of detoxification processes. Prevalent fungal detoxification pathways for aromatic compounds include the formation of sulfated and glycosidated conjugates. Such fungal metabolism has been extensively studied as models of mammalian metabolism. Furanocoumarins, a class of aromatic compounds, are important due to their biological activities and clinical applications. The 6',7'-dihydroxybergamottin (DHB), 6',7'-epoxybergamottin (EB), and bergamottin (BM) are three major furanocoumarins in grapefruit and their metabolism in humans is involved in the "grapefruit/drug interactions". Thus far, the metabolism by fungi of these furanocoumarins has received little attention. In our study, the metabolism by Aspergillus niger of DHB, EB, and BM has been investigated. A. niger was observed to metabolize EB, DHB, and BM into a water-soluble sulfate conjugate possibly using etherase-like and sulfotransferase-like enzyme activities. In addition, A. niger showed a specificity in metabolizing furanocoumarins, in which the fungus metabolized bergaptol and xanthotoxol into sulfate conjugates but did not metabolize 5-methoxypsoralen and 8-methoxypsoralen. These sulfate conjugates, i.e. bergaptoyl sulfate and xanthotoxoyl sulfate, were characterized by UV spectra, mass spectrometry, and acid hydrolysis.