The invention of the polymerase chain reaction (PCR) eventually earned Kary B. Mullis half of the 1993 Nobel Prize for Chemistry (1¿4). However, for several years, issues of quality control and reproducibility interfered with attempts at commercial or clinical application of PCR. More recently, persistent work and numerous methodological inno- tions and refinements have resulted in the establishment of PCR as a routine, sensitive, and specific detection method in hospital and agricultural labora- ries. This transformation of PCR from an experimental research technique to an established bioassay tool formed the impetus behind PCR in Bioanalysis. PCR has proven particularly valuable in clinical microbiology and the diagnosis of infectious diseases in humans and animals. This large and diverse group of applications is reviewed in Chapter 1 by Gorm Lisby. S- cific organisms now detectable by PCR include hepatitis C virus (protocols presented in Chapter 14), Mycobacterium tuberculosis (Chapter 18), Chla- dia and Trichomonas species (Chapter 20), Toxoplasma gondii (Chapter 17), Legionella species (Chapter 15), enterotoxigenic Escherichia coli (Chapters 9 and 10), HIV-1 subspecies (Chapter 8), bovine immunodeficiency-like virus (Chapter 6), rodent parvoviruses (Chapter 2), Ross River virus (Chapter 12), and porcine reproductive and respiratory syndrome virus (Chapter 7).