AbstractThe present study is part of an investigation of growth inhibition mechanisms inPicea abiesagainstFomes annosusand is concerned with the induction of ectolaccase activity inFomes annosus(3 strains) grown on cellobiose and ligninsulphonate and a 1:1 mixture of these substrates. It is shown that mycelial growth is almost independent of the substrates used. In two of theF. annosusstrains laccase is induced only by the use of ligninsulphonate whereas in the third strain it seems to be constitutive produced, which means that the laccase production is independent of the substrate.