This method provides an indirect measure of the relative bleachability, or residual lignin content of pulp. It may be used for all types and grades of chemical and semi-chemical unbleached and semi-bleached wood pulps obtained in yields under 60%. The method may also be used as a laboratory control technique for well screened pulps obtained in higher yields up to 70%. It should be noted that reproducibility is less for high yield pulps than for low yield pulps.