Xylanase treatment improved the bleachability of softwood kraft pulp both in conventional chlorine bleaching and in peroxide delignification. The mannanase isolated from Trichoderma reesei acted differently and improved the bleachability in the peroxide delignification significantly more than in the chlorine bleaching. When mannanase and xylanase were dosed together a positive effect was detected in both bleaching sequences. The reason for the different efficiencies of these enzymatic treatments in the bleaching may be the selectivities of the bleaching chemicals. The mannanase could hydrolyze amounts of glucomannan comparable to the xylan hydrolyzed by xylanase, suggesting that at least part of both hemicelluloses are located on the surface of the fibres.