As part of this lecture, a case study on recurring microbiological contamination in the manufacturing process of a sterile drug will be discussed. Due to incorrect identification of the contaminating microorganism, the source of the contamination could not initially be determined. CAPA measures were therefore taken, which were unable to prevent the contamination from reoccurring. Only through the use of more precise and reliable identification methods could the microorganism be accurately identified. This change made it possible to determine the cause of the contaminations and to organize activities that could prevent further contaminations with this microorganism.