Summary The polymerase chain reaction (PCR) permlts the in vitro ampliflcation of selected nucleic acid sequences with great sensitivity and specificity. Numerous applications of the method have been reported for the basic research in microbiology and PCR is already considered as a major advance in this field, complementary to that provided by genetic engineering techniques. In parallel, multiple diagnostic applications have also been described for the detection of infectious agents with promising results. However, practical limitations such as the question of false results due to carry over and the interpretation of positive results are often encountered in trying to use PCR as a routine procedure. Many improvements are still necessary before measuring the real value of PCR in microbiological diagnosis.