Eighty-five different fungal strains mere screened for the presence of amine oxidase after it was induced by n-butylamine, methylamine or spermine. Amine oxidase activity mas detected in all Aspergillus, Penicillium, and most of Monascus strains, as well as in Pullularia Doratomyces, Armillaria, Fusarium, Gibberella, Sporotricus, Trichophyton, Beauveria, Caldariomyces, Helicostylum, and Trichoderma, but not in Mucor, Neurospora, Syncephalis, Keratinomyces, Eurotium, Zygorhynchus, or Cladosporium, By electrophoresis of native proteins with amine oxidase activity staining, two to three different enzymes mere found in most of the strains. Predominant among these were copper-containing amine oxidases (EC 1.4.3.6), which were defected by Western blotting with polyclonal antibody against copper amine oxidase from Aspergillus niger AKU 3302. On SDS-PAGE, most of the enzymes showed bands corresponding to a molecular mass of about 75 kDa. Enzymes that did not react with the antibody against copper amine oxidase did not react either Pith the antibody against flavin-containing monoamine oxidase from Micrococcus luteus. However, the enzymatic activities of extracts that contained non-copper amine oxidases was substantially decreased by pargyline, an inhibitor specific to flavin-containing amine oxidases. Therefore, these enzymes are thought to belong to the class of flavin-containing amine oxidases (EC 1.4.3.4). Besides amine oxidase activity, increased aldehyde dehydrogenase activity was found in selected strains after induction with amines, from which it is supposed that amines are degraded via aldehydes to corresponding carboxylic acids, Two alternate metabolic pathways are suggested for methylamine and for larger aromatic amines.