Although research does not prove that drug use causes crime, it shows that when a person is actively using drugs, the number of crimes committed is significantly higher than that committed by nonusers and by the same person when not on drugs. The criminal justice system can thus reduce crime by curtailing drug use among offenders. The Drug Use Forecasting Program (DUF) can assist in this effort. DUF, begun under NIJ sponsorship in 1987, involves obtaining anonymous and voluntary interviews and urine specimens from a sample of people arrested in 22 large cities. DUF has shown a high degree of drug use among arrestees and diverse patterns of drug use among the cities sampled. Drug testing of arrestees and offenders could be used by the criminal justice system to document and monitor drug use by those on pretrial release and probation. Drug treatment programs could be mandatory for drug-using offenders. Offenders and pretrial releasees who continue to test positive for drugs could receive increasingly restrictive sanctions to deter them from continued drug use. Such efforts should reduce the number of crimes.