The technique of in situhybridization, in its various forms, has been usedroutinely in many laboratories for a number of years. In the post-genome era,gene arrays and proteomics have allowed us to identify hitherto unknownunrecognized pathways and mechanisms. However, rather than diminish theimportance of in situhybridization, the now widespread use of screening tech-nologies has increased the need to temporally and spatially localize the distri-bution of mRNA expression