AbstractNorway spruce specimens 50x30x30mm with initially determined ultrasonic characteristics in the longitudinal, radial, and tangential directions were subjected to bio-attacks with the brown-rot fungi Serpula lacrymans, Coniophora puteana,or Gloeophyllum trabeum, and the white-rot fungus Trametes versicolor, respectively. Bio-attacks lasted 4, 8, 12, or 16 weeks. Decreases of the ultrasonic wave velocities (Dc) and the dynamic modulus of elasticity (DMOEd) depended more or less closely on the enlarged degrees of rot in the spruce wood, and as the dynamic modulus of elasticity decreased approx. 1.7 to 2.3 times more than corresponding weights (Dm from 2.01 to 42.35%) or 2.1-3.4 times more than corresponding densities (Dr from 2.42 to 26.63%). Two sample t-test analyses of slopes “a” in the linear regressions Dc or DMOEd = a.(Dm) or a.(Dr) showed that drops of the ultrasonic and elastic characteristics of wood having the brown rot were not influenced by the fungus species. On the other hand, the velocity of ultrasonic waves in the longitudinal direction and the dynamic modulus of elasticity appeared to be suitable for distinguishing the brown rot from the white rot at known decreases of wood density. The anatomical direction of wood was a significant factor only for the white rot, when approx. 2-times higher decrease of the ultrasonic wave velocities was determined in the radial and tangential directions compared to the longitudinal one.