described in example 5 subsequent to the sulphite pretreatment the pulp was washed in a continuous pressure diffuser prior to the addition of oxygen and alkali in amounts of 39 kg o 2 and 44 kg naoh respectively per ton of 100 pulp oxidized white liquor was used as an alkali source the reaction conditions in the oxygen alkali stage were otherwise the same as described in example 5 after the oxygen alkali delignification the pulp was washed and the kappa number was determined the kappa numbers are given in the table as seen from the examples an increased kappa number reduction is obtained in the oxygen alkali pretreatment when the pulps are pretreated with a sulphite solution at a given kappa number of the unbleached pulp considerably lower kappa numbers can be obtained after an oxygen alkali delignification if the pulp has been pretreated with a sulphite solution when the pulp is bleached with chlorine containing chemicals the increased kappa number reduction in the oxygen alkali stage means that the consumption of bleaching chemicals can be substantially reduced additionally the effluent of chlorine containing waste liquors is reduced thus the sulphite pretreatment leads to an environmental advantage if the kappa number after the oxygen alkali stage is maintained constant the pretreatment of the pulp with a sulphite solution prior to the oxygen alkali delignification stage implies that the kappa number of the unbleached pulp can be increased table______________________________________sulphitecharge kg so sub 2 per kappaton of un kappa number numberbleached pulp unbleached o sub 2 bleached reduction______________________________________control 0 62 2 42 2 20 0example aexample 1 10 62 2 37 4 24 8example 2 30 62 2 34 9 27 3control 0 98 3 50 5 47 8example bexample 3 10 98 3 47 4 50 9example 4.