Longitudinal research on the course of dual disorders in clients who received treatment from the traditional parallel service system indicated a very slow rate of recovery, with usually less than 5 percent becoming abstinent each year. Growing discontent with the parallel treatment approach rapidly led to the development of a broad-based model that sought to improve outcomes by integrating mental health and drug abuse treatment. Preliminary studies employing a range of different integrated treatment models have yielded better outcomes than those traditionally produced by the parallel service system. Despite hopeful findings of these studies, many questions remain about integrated treatment that concern difficulties in comparing parallel and integrated treatment programs, effects of group interventions for dually-diagnosed clients, and the comparative efficacy of different integrated treatment models. Data from the New Hampshire dual disorders study, one that used intensive case management teams based on the Assertive Community Treatment model, are provided. 76 references, 2 tables, and 2 figures