Wood samples were taken from Norway spruce (Picea abies) in Switzerland with an increment borer and incubated on a selective medium. Basidiomycetes could be isolated only from 38% of the spruce cores with  macroscopically visible decay (17% Heterobasidion annosum, 12% Armillaria spp. and 9% other species).  Mortierella spp. were also frequently isolated. The problems associated with the isolation of decay fungi from boring cores are discussed.