[Polymerase chain reaction--principles and clinical relevance].

Molecular hybridization analyses and polymerase chain reaction (PCR) have substantially contributed to the diagnosis of infectious, genetic and malignant hepato-/gastroenterological diseases. While not generally informative, the detection of hepatitis-C-virus (HCV) RNA by PCR is at present the only means to demonstrate active HCV replication. Furthermore, PCR has for the first time allowed the identification of the infectious agent causing Morbus Whipple (Tropheryma whippleii), the noninvasive molecular detection of familial adenomatous polyposis (FAP) as well as of K-ras mutations in stool from patients with colorectal cancer. While in principle exquisitely sensitive and specific, PCR is a complex technique with a substantial risk and false-positive results, respectively. With a better understanding of the molecular pathogenesis, PCR-based diagnostics will be of increasing clinical significance for the sensitive and early detection, prevention or curative therapy of hepato-/gastroenterological diseases.