Two non-allelic laccase genes (lcc1 and lcc2) in Agaricus bisporus have been mapped to the same cosmid clone and are close together, in tandem. The intergenic region consists of 1562 bp between the stop codon of lcc1 and the start codon of lcc2. Differences between the 5' non-coding regions of the two genes suggest the potential for their differential regulation. By employing competitive RT-PCR and specific primer pairs that discriminate between lcc1 and lcc2, it has been shown that the level of lcc2 mRNA is approximately 300 times higher than that of lcc1 mRNA in malt extract liquid cultures; in compost cultures lcc2 mRNA is almost 7000 times more abundant than lcc1 mRNA.