Cognitive-behavioral therapy has a substantial evidence base with regard to its effectiveness for individuals with chronic pain. Historically, although there has been some investigation in to the processes by which treatment succeeds or fails, few data are available regarding the unique contributions of processes from distinct cognitive behavioral approaches and how these processes may interact to affect patient functioning. The present investigation Sought to evaluate three proposed process variables that have garnered empirical Support within chronic pain settings, namely: pain intensity, catastrophizing, and acceptance. Participants were 252 consecutive patients who completed treatment on an interdisciplinary pain management unit. Using multiple regression, the contributions of changes in process variables to changes in treatment outcomes were assessed. In general, changes in both acceptance and catastrophizing accounted for significant variance independent of, and larger than, that accounted for by change in pain intensity. Changes in acceptance and catastrophizing accounted for roughly equivalent amounts of variance when entered immediately following changes in pain, and when entered following one another. The potential impact of these results is discussed in relation to the particular treatment delivered. Issues relating to change at the level of frequency or content of psychological experiences are considered relative to change in the functions of these experiences.