The 720 subjects consisted of two groups of male and female methadone maintenance patients selected from several California clinics, interviewed 3.5 years and 6 years after their admission, respectively. The data were collected through retrospective longitudinal interviews. The independent variable in the study was legal supervision; the dependent variables were narcotics use, other drug use, criminal behavior, social functioning, and treatment. The findings indicate that legal supervision with urine testing was effective in reducing daily narcotics use, property crime, and drug trafficking offenses among all groups. The effectiveness of urine testing and level of legal supervision were both differentially affected by sex and ethnic group. Some of the differences may be attributable to different levels of time on methadone treatment. 6 tables, 5 figures, 2 notes, and 37 references.