Abstract: Disclosed is a method of detecting the presence in a sample of a polypeptide exogenously administered to a mammalian subject from whom the sample is obtained, and distinguishing between such an exogenously administered polypeptide and a naturally-occurring endogenous polypeptide present in the sample; the method comprising obtaining a sample from the subject; and subjecting the sample to analysis of fluorescence at a suitable wavelength; wherein the exogenously administered polypeptide is tagged with a greater or lesser amount of fluorescence activity, relative to the untagged endogenous polypeptide, at the wavelength(s) analyzed.