This study was based on a longitudinal cohort design commonly used in substance abuse research for the collection of "natural history" data. The study was designed to provide a retrospective account of drug use and treatment effects by using subjects as their own controls for changes over time; thus, the study was quasi-experimental and did not have a matched control group for comparison purposes. The longitudinal cohort design maximized external validity by targeting one cohort of clients in several Los Angeles County substance abuse facilities in 1996. Use ecology data included MA varieties and street names, first introductions to use, drug-use histories, access, selling and manufacturing, routes of administration, unwanted results of use, and participants' use behavior in the year before the 1996 treatment. Information on motivation for using MA indicates that clients used MA as a substitute for other stimulants; to cope with mental distress; to stay awake; to enhance sexual experience; and to lose weight. Two case studies are presented to provide a more holistic portrait of clients who are struggling with MA abuse, so as to present two motivation categories (cope with mental distress and as a sexual stimulant) that present special challenges for treatment intake counselors. 8 references