Spruce wood that had been degraded by white-rot fungi (Trametes versicolor or Ceriporiopsis subvermispora) and suffered mass losses up to 17% was investigated by transmission Fourier transform infrared (FT-IR) imaging microscopy. A significant marker during incipient simultaneous white-rot (T. versicolor) was the cleavage of glycosidic bonds of polysaccharides that preceded their metabolisation. Simultaneous white-rot processes were also characterised by a relative decrease of the overall lignin content and a relative accumulation of wood polysaccharides. No early marker was found for selective white-rot (C. subvermispora) that removes mainly lignin by an oxidative process. This feature was detected only in wood samples exhibiting mass losses higher than 12%. Furthermore, it was shown, that simultaneous and selective white-rot processes were unevenly distributed within the wood samples but quite evenly distributed within single tracheids.