Wood degradation by the white-rot basidiomycete Inonotus hispidus was studied in ash ( Fraxinus excelsior ) and London plane ( Platanus × hispanica ). After 6 or 12 wk incubation of inoculated wood blocks the loss of dry weight was greater in plane than in ash, corresponding with a more intense visible degradation of the secondary walls in the lignified axial cells. Atypically for a white-rot, degraded cell walls contained internal cavities. The cells thus affected were the late-wood fibres in ash and the fibre tracheids in plane. The structure of the cavities and the formation of multiple T-branches by the associated hyphae were typical of a soft-rot normally associated with certain Deuteromycotina and Ascomycotina. Naturally infected wood from a living plane tree contained cavities identical to those found in the wood blocks, and also showed typical white-rot degradation where the decay was more advanced, with dissolution of the middle lamellae and the induction of progressive wall thinning by hyphae in the lumina of axial and ray cells. In the inoculated blocks, only ash showed degradation of ray cells, even after 12 wk incubation. Another form of degradation, observed in the early-wood fibres of the ash blocks, was notch-erosion at the cell wall/lumen interface, typical of both white-rot and some soft-rot fungi.