Paper production requires fibres to be refined, meaning mechanically treated to present sufficient bonding potential. As it is a highly energy consuming stage, various charges of cellulase as a pre-treatment were investigated to reduce the energy consumption and improve paper properties. The enzyme was added during pulp slushing and conditions of treatment were chosen to be compatible with an industrial application. Results obtained after low consistency disc refining of a softwood bleached kraft pulp were compared at a given drainage index. Enzymatically-treated samples showed a better development of fibrillation leading to a stronger paper. Moreover, fibre swelling was significantly improved. The impact of cellulase charge added to the pulp was identified. However, for all cellulase charges tested, fibre intrinsic resistance was lowered. Consequently fibres became shorter and tear index dropped. A solution was found by applying a milder treatment consisting in reducing refining intensity. This was a way to limit the intense fibre cutting at high refining levels. Moreover, by treating pulp with cellulase, it became possible to reduce refining intensity by 33%, keeping breaking length similar to control. (C) 2010 Elsevier Ltd. All rights reserved.