The ability to amplify genetic material using PCR has transformed the field of diagnostics. Now any organism can be detected by identifying the presence of specific nucleic acids. However, there still remain areas in which traditional PCR cannot easily be applied. In this chapter, we describe a different flavour of PCR in which an enzyme acts on a DNA substrate to convert it into a DNA product that can be detected by PCR. This opens up new areas for the application of the PCR technique and we will show how the technique can be used to detect immunoconjugates, bacterial drug resistance, and bacterial contamination.