In an experiment established on three Norway spruce sites in southern Sweden, the ability of five strains of Phlebiopsis gigantea , including the commercial strain Rotstop®, and two Trichoderma formulations to control natural Heterobasidion spp. spore infections was compared. At each site 160 trees were felled, and the resulting stumps were treated with spore suspensions of the seven fungal preparations. Twenty stumps at each site were left untreated as control stumps. When sampled 9 months after treatment, two of the P. gigantea strains (1984 and 1985) were the most effective at preventing infection by Heterobasidion spp. The other three P. gigantea strains were less effective, and two Trichoderma formulations did not significantly reduce Heterobasidion spp. infections.