A decade after the first studies were performed it is justifiable to claim that molecular techniques have revolutionised the work of the clinical virology laboratory. Hitherto, the role of the virology laboratory was often a retrospective diagnosis based on virus isolation and serology. Nevertheless, the epidemiological data collected in this way justified the continued activity of clinical virology. The recent molecular revolution in laboratory methods has been timely because it has been in parallel with the emergence of new pathogens that have presented the clinical virologist with fresh diagnostic challenges. A concurrent development of specific antiviral compounds has increased the potential of rapid laboratory investigation to contribute to the management of acutely ill or immunosuppressed patients.

Molecular assays for the detection of microorganisms can be designed even when only partial nucleic acid sequence information is available. This is valuable when identifying and diagnosing new diseases and emerging pathogens because there is the possibility of a rapid development of assays in house. However, the standardisation of assay design is a continuing problem because of the large number of nucleic acid sequences that can be used as a target for the detection of any one virus. Many of the methodologies associated with molecular techniques have now been incorporated into commercial kits, but in house molecular assays continue to be used. In house assays are often well evaluated and perform to a high standard, but differing assay sensitivities and specificities have been highlighted by quality assessment programmes. Some of the variations in performance can be accounted for by assay design, although it is probable that some in house assays do not travel well and perform badly because laboratory staff are inexperienced with molecular techniques. Molecular techniques in their present format, even in commercial kits, require a considerable degree of operator skill. If a …