Manufacturing of mechanical pulp is a very energy-consuming process. Application of enzymes to wood chips is an attractive alternative to decrease energy demand in the refining process and to introduce novel functional properties on fibers. A variety of enzymes were applied to plug screw compressed chips in order to improve enzyme access onto wood fibers. Consumption of refining energy was examined with a laboratory low-intensity refiner after 6-h enzyme treatments with manganese peroxidase (MnP), laccase-mediator system, pectinase, or a cellulase mixture. The results were compared to biopulping with the white-rot fungus Physisporinus rivulosus. Specific energy consumption resembling the first-stage refining was measured, and chemical modifications on the fibers were evaluated. The specific energy consumption in the refining of Scots pine wood chips treated with MnP decreased about 11% when compared to the untreated reference chips, and in the refining of Norway spruce somewhat less, 6%. Fungal pre-treatment resulted in similar energy savings on spruce as MnP treatment did. Hydrolytic enzyme and MnP treatments on pine resulted in similar energy savings on average, though the hydrolytic enzyme treatments at their best reached to about 15% energy savings. Polyelectrolyte titration indicated increased surface charge in the case of MnP treated pine pulps, which were refined to low freeness values (CSF 85-130 ml). Most laboratory handsheet properties, i.e. strength, light scattering and opacity, were improved at given specific refining energy. Only brightness was slightly decreased. The MnP treatment seems to be a promising concept for energy savings and fiber surface modifications. (C) 2007 Elsevier Inc. All rights reserved.