Lentinula edodes (Berk.) Pegler was cultivated in liquid media containing malt and yeast extract. Extracellular laccase activity, measured in the culture fluids, was 5-18 times higher in cultures incubated for 29 days than in cultures incubated for 24 days. The addition of water-soluble lignin derivatives or Trichoderma sp. in cultures of L. edodes incubated for 11 days increased laccase activity 3- to 20 fold. The higher response was obtained with live mycelium of Trichoderma sp., but cell-free culture fluids of Trichoderma sp. in pure cultures were also effective. Trichoderma sp. induced changes in the laccase isoenzyme pattern as a result of the alteration of laccases secreted by L. edodes and not the induction of new isoforms.