Ninety volunteers in a media organization were randomly allocated to an Acceptance and Commitment Therapy (ACT, n = 30) group that sought to enhance people's ability to cope with work-related strain, an Innovation Promotion Program (IPP, n = 30) that helped individuals to identify and then innovatively change causes of occupational strain, or a waitlist control group (n = 30). Both interventions lasted 9 hr, spread over 3 months. Improvements in mental health and work-related variables were found following both interventions. As hypothesized, changes in outcome variables in the ACT condition were mediated only by the acceptance of undesirable thoughts and feelings. In the IPP condition, outcome change was mediated only by attempts to modify stressors. Discussion focused on the importance of understanding the mechanisms underpinning change in occupational stress management interventions.