Data were obtained from longitudinal interviews with 720 heroin addicts who entered methadone maintenance programs in Southern California during the 1971-1978 period. Five variables were derived by aggregating information from over 600 drug addiction histories averaging 12 years in length. These variables included abstinence from drug use, daily drug use (or addiction), property crime, methadone maintenance treatment, and legal supervision. Overall, system dynamics among the variables were characterized by long-term rather than short-term relationships. Neither methadone maintenance nor legal supervision had short-term effects on drug use or property crime. Methadone maintenance treatment demonstrated long-term benefits by reducing drug use and criminal activities. Legal supervision, on the other hand, did not reduce either drug use or property crime in the long run. Instead, there was a positive long-term relationship in which a higher level of legal supervision was related to higher levels of drug use and criminal activity. This latter finding is consistent with the observation that either drug use or criminal activity is likely to bring addicts to the attention of the legal system. Addicts as a group, however, did not directly respond to legal supervision by changing their drug use or crime involvement except perhaps through coerced treatment. Policy implications of the findings and areas for further research are discussed. 24 references, 3 tables, and 1 figure (Author abstract modified)