The data indicate the popularity of a particular drug, such as cocaine, emerges within a limited subpopulation. Drug epidemics tend to be local, with drug popularity varying substantially across jurisdictions. As of 1996, for example, crack use was declining at most DUF locations. In some noncoastal cities, however, the crack epidemic appeared as strong as ever. The data also show information about the prevalence of certain drugs, such as those monitored by DUF, can help identify drug epidemic phases experienced by a community. In addition, changes in drug use by young people indicate important transitions in a drug's popularity. To the extent future drug epidemics are similar to the crack epidemic, agencies can use DUF data to better deploy drug control resources. 16 references, 11 notes, 1 table, and 25 figures