The work constitutes the most comprehensive evaluation of methadone maintenance treatment in the United States to date. Based upon three years of data collection at drug abuse treatment programs in New York City, Philadelphia and Baltimore, the study contains findings for 617 male intra- venous addicts, interviewed during and after six methadone programs. The major findings of the project concern the effectiveness of methadone maintenance in reducing drug use, crime and other deviant behavior, the effectiveness of cer- tain programs as compared to others, the pressing need to improve the quality of care at mostprograms and the estab- lishment of successful procedures and methodology for evalu- ating drug abuse treatment programs.