Pectinase, purified from the commercial enzyme mixture Novozym 863 by affinity chromatography, was able to lower the cationic demand of peroxide-bleached mechanical pulp. It was also able to enhance the ability of cationic polymers to increase fines and ash retention. A second purified pectinase, cloned polygalacturonase I from the fungus Aspergillus aculeatus, also produced these effects. However, when applied at the same pectinase activity, the crude pectinase increased retention more than the purified polygalacturonase. Apparently, other enzyme activities in Novozym 863 contribute to its effects on retention. This research expands our understanding of pectinase activity by proving that pectinase is responsible for both reducing cationic demand and improving the retention of peroxide-bleached thermomechanical pulps. (C) 2004 Elsevier Inc. All rights reserved.