Drug use in arrestees is more than 10 times higher than is reported in household or senior high school surveys. In 1986, the National Institute of Justice began the Drug Use Forecasting program in New York City. The DUF is designed to provide each city with information for detecting changes in drug use trends of arrestees. With DUF data, research is possible into the prevalence of drug use among criminal justice populations, cyclical trends in drug use, the age of onset and progression of drug use, the relationship of drug use to crime type, the validity of arrestees' self-reports and the AIDS risk behaviors in arrestees. The program can be used to measure impact of local drug use reduction efforts and plan the allocation of law enforcement treatment/prevention resources. This report includes the results from 16 cities; 22 cities have joined the program, and information from them will be available in future reports. 4 tables, 5 figures.