The primary goal of a process evaluation is to establish and maintain program integrity. It ensures that a program is implemented according to the intended criteria and is achieving its objectives. Process evaluation consists of an ongoing review of the program's operational procedures, which are adjusted to evaluation outcomes. Procedures used in the process evaluation include site visits, group meetings, training programs and workshops, data collection and analysis, and indispensable program adjustments. As drug treatment programs within prisons become more likely, the need to conduct scientific outcome evaluations becomes imperative; however, as a history of such research efforts builds, it is increasingly evident that the structure and functioning of the program in its early stages in relationship to the important groups in the program establishment are crucial to generating reliable and valid outcome data. As part of the process evaluation, five groups within the correctional setting need to be considered: inmates, treatment staff, prison staff, prison administration, and the parole board. These five groups are discussed in this article relative to three stages of development of substance abuse treatment in prison: program policy making, evolution, and viability. 10 references