Two chemical bleached pulps were treated with a crude enzyme mixture in the presence of HgCI2, (1 mM). Such treatment inhibited endo-cellulases. Xylans were- thus subjected to selective in-situ hydrolysis. The enzyme-treated pulps car. be compared to slightly beaten pulps. The modified fibers show external fibrillation and reveal strong beatability. Therefore, a decrease in energy demand can be gained in the papermaking process.