The interaction of cultures from the recombined mycelia of the fungus Fomitopsis pinicola (Sow. ex Fr) Karst. was studied on PDA medium. The cultures were isolated from different carpophores and from different segments of the same carpophore originating from a felled beech tree. The interactions show that recombined mycelia of this species can be divided into numerous incompatible physiological "races" or "pathotypes", distinguished also by morphological features of the mycelia.