The introduction and increasing usage of nucleic acid based methods in clinical microbiology over the last years have contributed to better and earlier diagnosis of infectious diseases as well as more accurate monitoring of treatment. Various nucleic acid amplification methods such as the polymerase chain reaction and the ligase chain reaction are widely used in Norwegian clinical microbiological laboratories to detect fastidious or non-cultured infectious agents. The amplification methods combine an extremely high sensitivity with acceptable specificity. About 200,000 nucleic acid based examinations are now performed in clinical microbiological laboratories in Norway each year.