At present, copper/quinone-containing amine oxidases (EC 1.4.3.6) are very intensively studied group of enzymes. They are contained in most of living organisms, taking part in significant physiological processes. They use copper and topa quinone (2,4,5-trihydroxyphenylalanine quinone) derived from its tyrosine precursor as the redox cofactor. Substantial progress in the study of these enzymes has been achieved in past five years. The most important achievements involving enzyme structure and reaction mechanism are shown in relation with the enzymes from particular sources. Recently, DNAs/cDNAs for several of these enzymes have been cloned and sequenced, which together with other data allows us to indicate conserved amino acid residues essential for the enzyme function. Computer alignment of 13 known sequences is presented and structure implications are discussed.