Aryl-alcohol oxidase (AAO), an extracellular enzyme characteristic of fungi from the genus Pleurotus, constitutes a source for H2O2 required in lignin biodegradation. The gene aao has been cloned, sequenced and characterized for the first time in Pleurotus eryngii. Both cDNA and genomic libraries were screened with probes obtained by PCR using as primers oligonucleotides corresponding to the N-terminus and internal sequences of AAO. DNA sequences from positive clones showed a unique open reading frame of 1779 nucleotides interrupted by 12 introns. The conceptual translation of the protein agrees with the partial amino acid sequences obtained from protein sequencing. A search for proteins with related amino-acid sequences revealed that glucose oxidase from Aspergillus niger has 33% identity and 51% similarity. A comparison with other oxidoreductases showed common motifs in both N- and C-terminal regions corresponding, respectively, to the FAD-binding region and the enzyme active site. However, AAO probably has structural differences with other oxidases, as deduced from its unique ability to generate H2O2 from the oxidation of aromatic alcohols.