A method for determining the amount of glycated hemoglobin (HbA1c), in which—if required—the erythrocytes in a sample are hemolyzed, the haemoglobin that is then released—if required—is contacted with a proteolytic agent and the glycated hemoglobin degradation products obtained in this way or otherwise are quantified is disclosed. In order to provide such a process and reagents employable therein that has/have the property of sufficient stability of the chemical compounds that are essential to the reaction, the provision of the requisite proteolytic agent in the form of an inactivated protease is proposed, which is then only reactivated in situ. For the stabilization of the hemoglobin, which is unfolded at a very low pH in the range from 1 to 3, at least one suitable stabilizer should be present in the hemolysis solution, and, where a leuco dye is used in connection with the determination of the amount of HbA1c, it is proposed that the latter be stabilized with particular phosphine compounds and/or thio compounds.