The expression of laccase in the white rot fungus Trametes versicolor is regulated at the level of gene transcription by copper and nitrogen. We used reverse transcription-PCR to demonstrate that as the concentration of copper or nitrogen in fungal cultures was increased, an increase in laccase activity, corresponding to increased lactase gent! transcription levels was observed. In addition. we demonstrated that the amounts of lactase mRNA and laccase activity in 10-day-old cultures were a direct function of the concentration of either 1-hydroxybenzotriazole, a previously described lactase substrate, or 2,5-xylidine, a well-known lactase inducer, in;he medium. 30 induction was observed after the addition of two aromatic acids, ferulic acid and veratric acid, which have been shown to induce laccase production in other white rot fungi. When either copper, 2,5-xylidine, or both compounds were added to cultures grown in the absence of copper, increased laccase transcript levels were detected within 15 min. Corresponding increases in laccase activity were observed after W-h incubation only when copper was present.