The Human Genome Project, an endeavor to map and sequence the entire human genome, has been in existence for almost seven years. One result of this effort has been the development of increasingly detailed genetic and physical maps spanning large regions of virtually every chromosome. Paralleling this has been the increasingly high resolution mapping of many &wnetic diseases. Together, these developments have facilitated the isolation of specific disease genes and are now motivating the construction of comprehensive transcriptional maps. This latter endeavor represents a new facet of the...