Impregnability of poles and other products made from spruce or fir wood decreases after the closing of toruses in the pits of tracheids, which usually occurs after their drying up to the fiber saturation point. With the aim of reopening access to the pits in the tracheids, the microscopic fungus Trichoderma viride was used for the enzymatic degradation of the pits in Norway spruce. During the summer, freshly cut and debarked spruce bolts were exposed in an inoculation mycelium of T. viride for 1, 3, 6, and 9 weeks under exterior conditions. Very good permeability and impregnability of spruce sapwood was observed after 1 or 3 weeks with no apparent change in its mechanical properties (Modulus of Rupture, Impact Bending Strength). On the other hand, previously closed pits of spruce heartwood remained unchanged in all experiments. Generally, coming out from achieved results and knowledge of other researches, bio-treatments of conifers are suitable for improving the impregnability of poles and other rounded timber products with the sapwood zone intact. However, bio-treatments for squared timbers with visible heartwood are usually a less appropriate.