The degradation of polycyclic aromatic hydrocarbons was investigated with aquatic hyphomycetes isolated from extremely heavy metal polluted water. Liquid cultures of the aquatic hyphomycete Heliscus lugdunensis degraded 1-naphtol. 1,4-Naphthoquinone and 1-naphthylsulfate were identified as degradation products. In addition, a novel metabolite was identified as 1-methoxynaphthalene, employing highperformance liquid chromatography (HPLC) and gas chromatography - electron impact mass spectrometry. Upon HPLC and HPLC combined with electrospray ionization mass spectrometry evidence for a further transformation product, most likely 4-hydroxy-1-naphthylsulfate, was obtained. In contrast, no glucuronide and glycoside conjugates could be detected. Accordingly, neither UDP-glucuronosyltransferase nor UDP-glycosyltransferase showed activity towards 1-naphtol. Fungal degradation of naphthalene has been described to proceed via the intermediates 1-naphthol and 1,4-naphthoquinone to 4-hydroxy-1-tetralone. The formation of 1,4-naphthoquinone from 1-naphthol by H. lugdunensis is thus in accordance with hitherto published data.