SUMMARY R-glucanase activities, and susceptibility of native-wall preparations to degrada- tion by R-glucanase, were determined in strains of Schizophyllum commune with three different mutations that disrupt nuclear migration. These mutations, MI I, MI^, and Mi6 appeared to affect the susceptibility of the hyphal wall to R-glucanase but MII and M15 also had an effect on the activity of R-glucanase. Both effects may be related to the stability of complex septa in these mutants and account for their specific mating behaviour.