This special issue arises from a meeting of the Royal Microscopical Society on 'Immunocytochemistry and Allied Techniques' held in Brussels in 1993 jointly with the Belgian Societies for Cell Biology, Clinical Cytology, Electron Microscopy, and Pathology. At that meeting, the European Immunocytochemistry Club was formed. Symposia were held on a range of technologies which utilized affinity binding of antibodies, nucleic acid probes, haptens and chemical probes for the specific localization of protein or nucleic acid targets. The meeting was very wide-ranging, covering subjects as diverse as 'tracking molecules in living cells', 'clinical cytology', 'cell differentiation and the tumorigenic process' and 'from the gene to the protein: skeletal muscle as a model system'. Although there was no specific session devoted to in situ hybridization there were many papers presented within the symposia and the accompanying poster sessions which depended to a greater or lesser degree upon this technique. It is this level of interest that gave rise to the concept of producing a special issue of the Histochemical Journal. The aim of this issue is to draw together these disparate research disciplines and present an overview of the range of techniques and applications which form the method that has come to be known as in situ hybridization.
At Brussels it became clear that a major sea-change had taken place in the development of in situ hybridization over recent years. It was obvious to all who attended that the method could no longer be considered simply as a research tool to be used only by an 61ire band of dedicated aficionados but rather had become a robust tool which could be used in a wide range of situations, including some applications which were dependable enough to be considered for use in the routine clinical environment. For many years those who have watched the development of in situ hybridization from the outside saw a labour-intensive method more akin to a cottage industry than science. Success depended upon optimization over very many steps requiring repeated manipulation of tissue sections and application of a range of reagents. It was usually the case that localizations took two days and that many controls were required in order to validate the results. In addition, molecular biologists were not initially comfortable with the demands of histology, and the histologist often found the world of molecular and microbiology a mystical place where you deal with probes which you cannot see which need labelling using enzymes which are also invisible. If, to all this, is added a natural dislike of radioisotopes, it is hardly 0018-2214 9 1995 Chapman & Hall