DARP showed that methodologically rigorous longitudinal field-based research could be successfully conducted with this difficult population (drug abusers) to evaluate drug abuse treatment. Consequently, periodic national multisite evaluations of drug abuse treatment have become part of Federal research. TOPS was designed to provide longitudinal data on clients entering federally funded drug abuse treatment programs to allow assessment of short-term and long-term treatment outcomes. It was intended to expand on DARP by obtaining more data on patient attributes, program environments, and services delivered in treatment. Both DARP and TOPS showed that treatment was effective in reducing the use of heroin and other illicit drugs during and after treatment. DATOS was begun in 1989 to study drug abuse treatment in typical, stable programs to determine its effectiveness for current treatment populations and drug abuse patterns. In addition to examining contemporary treatment outcomes, DATOS will address the evolving drug abuse treatment system, factors related to engagement and retention, and long- term outcomes for a treatment sample, with attention to the use of drug abuse treatment and other health resources over time. 109 references