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Laccase is a multicopper-containing enzyme that catalyzes the oxidation of phenolic compounds. lcc1cDNA coding for a secretory laccase of Pycnoporus coccineuswas expressed under the maltose inducible amyBpromoter in Aspergillus oryzaeand under the galactose inducible GAL10promoter in Saccharomyces cerevisiae. Laccase activities, which were undetectable in the absence of copper, were observed by increasing copper concentrations in the media for both systems. The amounts of secreted laccase protein but not lcc1mRNA increased in proportion to copper concentrations in A. oryzae. The extracellular activities of native A. oryzaeamylase and recombinant RNase-T1 expressed from the same amyBpromoter in A. oryzaewere constant regardless of copper concentrations. Our results indicate that a high copper concentration is required for the production of active laccase in heterologous hosts and that the copper is required for a post-transcriptional process.