AbstractCharacterization of the dissolved and colloidal substances (DCS) in the process water of a bleached chemithermomechanical pulp (BCTMP) production line showed that the major lipophilic substances (wood resins) were dehydroabietic acid, linoleic acid, oleic acid, and palmitic acid. Model compound experiments indicated that polysaccharides contained in DCS had significant effects on the stability of the system. Effects of neutral and acidic polysaccharides on the stability of wood resins (model resin acid R and fatty acid O) in the presence of metal ions were then investigated. No calcium-induced aggregation occurred when the concentration ratio of added neutral polysaccharide to R and O exceeded 0.2 and 1.0, respectively. Acidic polysaccharide could further degrade the stability of resin dispersions in the presence of calcium ions and yet have a positive effect in the presence of only sodium ions.