A method is proposed for separating worn bank notes from a quantity of bank notes in bank note processing machines. A target rate cunfit,0 of bank notes to be separated is prescribed. The bank notes are assessed one after the other. In the process they are counted. Further, the value of at least one physical parameter of each bank note affected by wear is measured during the assessment. The measured value, or a value derived therefrom, of each bank note is compared with a threshold value during the assessment. If the threshold value is exceeded, the bank note in question is separated during the assessment. The separated bank notes are counted during the assessment. The threshold value is adapted after assessing each bank note or after a fixed prescribed number m>>n of bank notes by feedback control. The control parameter is the rate cunfit,i of the bank notes separated up to said bank note, and the set parameter is the threshold value.