The invention relates to prolyl endopeptidase (PREP) inhibitors which contain a condensed 2,4-dihydro-3H-1,2,4-triazol-3-one ring system, methods for producing same, the use thereof alone or in combinations for treating and/or preventing diseases, and the use thereof for producing drugs for treating and/or preventing diseases, in particular for treating and/or preventing inflammatory lung diseases (COPD).