The genetic load of three lowland populations of Osmunda regalis was studied. The presence of deleterious mutations was reflected in disturbances in gametophyte development sequences and in the course of gametogenesis and fertilization. In sporophyte generation, sporophytic lethals were expressed in the zygotic, embryonic, postembryonic or juvenile stages, causing lethality of homozygous individuals originating from selfing. Heterozygous individuals were symptomless carriers of this genetic load.