The studies compared the pretreatment behavior and posttreatment behavior among clients receiving various types of treatment for drug addiction and persons who received little or no treatment. Three hundred and sixty clients of Washington's Narcotics Treatment Administration during 1971-73 were divided into treatment groups (methadone maintenance or abstinence) and control groups. Their subsequent drug use, criminal activity, and productivity were studied before treatment and during short term and long term followup periods. Results showed that clients experienced major behavioral changes, although the effects of treatment could not be separated from other factors. Results also showed that clients did equally well whether they stayed in the treatment program 1 day or 5 years. Moreover, neither methadone maintenance nor detoxification was clearly superior to one another. In New York City, 782 clients of the Addiction Services Agency were studied. Treatments included methadone maintenance, ambulatory units, and therapeutic communities. Results were similar to those for the Washington, D.C., study. Following comparative analysis of the two studies, it was concluded that the similarities in the findings and their implications for treatment provide compelling reasons for other programs to consider them seriously. Furthermore, demographic and background factors did not explain behavioral outcomes and thus were of little predictive value. Results supported the existence of various types of treatments but did not indicate clear superiority of any specific treatment. Since time in treatment has no relationship to later change in client behavior, minimization of treatment time should be considered. Research should focus on the effects on outcomes of community attitudes, criminal justice system personnel attitudes, addicts' motivation on entering treatment, the intake process, and use of different comparison groups. Tables, client profiles, footnotes, and an appendix presenting additional data are included.