The colonization of wax impregnated pine sapwood (Pinus sylvestris L.) and beech (Fagus sylvatica L.) by blue stain fungi and their hyphal migration within the treated wood was investigated. Neither the hydrophobation effect nor the physical presence of the congealed wax deposits could impede fungal growth on the surface. However, in contrast to the untreated controls, there was a lower occurrence of hyphae in wax-treated wood. Blue stain fungi grew mainly near the cross cut as well as in empty spaces such as micro-capillaries, parenchyma tissue or other wax free zones of treated wood.