A national campaign to prevent the spread of AIDS requires the best possible estimates of the number, types and demographic characteristics of intravenous (IV) drug users so they can be reached by educational and preventive measures. The purposes of this project are to: conduct studies in six cities to determine the number, types, characteristics and locations of IV drug users at-risk for AIDS; develop new methods for analyzing and comparing the various empirical data sets in these cities; develop procedures by which such an analysis can be easily applied in other cities; determine where local analysts do excellent jobs in gathering, analyzing and reporting empirical data, and communicate these approaches to persons in other areas; provide the best possible estimates of IV drug users so that persons running prevention programs can better direct and evaluate their efforts; train persons in the methods developed during this project; and suggest improvements in data gathering that would provide better information in the future. During the project's first year, six types of existing data will be collected (Drug Abuse Warning Network, DAWN, Emergency Room mentions; drug treatment statistics; Center for Disease Control, CDC, AIDS surveillance data; drug arrest figures; AIDS seropositivity studies; and independent reports on sub-populations in which there are substantial numbers of IV drug users; reports will be written for three cities; and there will be a summary report describing our methods and results. During the second year, personnel in three other cities will be trained in the methods that have been developed so that they can write their own reports tailored to their city's data systems, problems and needs. These three city reports will be submitted at the conclusion of this project along with a final report detailing a format for identifying numbers, types and characteristics of IV drug users at-risk for AIDS in American cities.