Bleaching wood pulp with sodium hydrosulfite in the presence of hexamethylenetetramine

In a process for bleaching wood pulp with sodium hydrosulfite under anaerobic conditions at a temperature between about 90.degree.F and 180.degree.F and at a pH of between about 4.0 and 7.0, the improvement which comprises conducting the bleaching in the presence of at least about 2 weight percent hexamethylenetetramine based upon the weight of sodium hydrosulfite, said weight percent of hexamethylenetetramine being effective to prevent formation of hydrogen sulfide during sodium hydrosulfite bleaching of wood pulp.