Data came from the Arrestee Drug Abuse Monitoring program that evolved from the Drug Use Forecasting system in the United States. Information came from voluntary, confidential interviews and from urinalysis of arrestees held for 48 hours or less. Results from sites in the United States indicated that the extent of illicit drug use and the types of drugs consumed varied between sites. Data from the other countries also revealed that drug markets were localized, with variability in the percentage testing positive and in the types of drugs detected. The proportion testing positive for marijuana was substantial at all sites. Much greater variability existed in relation to opiates, amphetamines, and cocaine. Some Australian sites had among the highest rates of opiate use among detainees in the five countries. Findings suggested the need for research on barriers or protective factors to prevent particular markets from taking hold. Findings also indicated the reducing or even dismantling heroin markets should reduce rates of property offenses around those markets. Findings also indicated the need for ongoing research, monitoring, and intervention to address weaker drug markets when they appeared and for cooperation among health and police officers across bureaucratic boundaries to address drug problems. Tables and 20 references