Abstract: A method in bleaching of pulp is described, in which the pulp is subjected to a peroxide bleaching step, whereupon the pulp is washed and the washing liquid from the washing is separated from the pulp in the form of a filtrate. The method is characterised in that the filtrate is treated with an aluminium compound, such as aluminium sulphate or polyaluminium sulphate, for precipitation of interfering substances, such as oxygen-demanding organic material and metals, that the precipitated material is removed from the filtrate, that the aluminium content of the filtrate after precipitation of interfering substances is adjusted to at most 20 ppm, and that the filtrate is then recirculated to the peroxide bleaching step. By the method, a reduced consumption of hydrogen peroxide in the peroxide bleaching step is achieved.