This report presents initial results of the first phase of the Treatment Outcome Prospective Study (TOPS) a longitudinal investigation of the natural history of persons identified as eligible for treatment at selected federally-funded drug treatment programs in 1979-1981. The materials describe the characteristics, behavior, and intreatment outcomes of 3,389 treatment clients in 27 drug treatment programs in 6 cities in 1979. The analyses contain a basic description of the clients' characteristics and behaviors in the year prior to treatment and during their first year in treatment. A literature review, the research methodology, and several chapters reporting basic descriptive results on demographic and lifestyle variables are presented in terms of: (1) alcohol and drug use patterns, associated problems, and treatment; (2) mental health and treatment patterns; (3) illegal activity and criminal justice involvement; and (4) employment- and income-related activities. Data on treatment program services and client satisfaction with the services are highlighted along with the effects up to 12 months after treatment on the selected outcome measures of alcohol use, drug use, depression, illegal activity, and employment. The report concludes with a brief summary of major findings and suggestions of tentative implications. (Author/NRB)