The invention relates to a method for determining auto-antibodies (TRAb) to the TSH receptor (TSH-R), formed in a biological sample obtained from a patient. According to said method, the sample or at least one antibody fraction of the sample is reacted in a known manner in a reaction mixture in the presence of a first immunoreagent in the form of a selective competitor, with a second immunoreagent in the form of a TSH-R preparation. The selective competitor and/or the TSH-R preparation is/are, or can be labelled. The presence and/or quantity of the TRAb sought in the sample is determined by means of the bond between the TSH-R preparation and the selective competitor. According to the invention, the TSH receptor blocking auto-antibody (TBAb) is selectively determined in such a way, that the selective competitor is for the first time chosen to bond at those binding sites of the TSH-R preparation, for which said competitor competes with the TBAb that is to be determined, not however with the TSAb.