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Aim : Work stress and its impact on health have been widely studied. However, very few studies have examined the effect of implementing measures designed to reduce work stress, a risk factor for psychological health problems. The purpose of this study was to fill this gap. Methods : Two surveys were conducted in October 2009 and October 2011. 150 employees participated in the first trial, while 108 took part in the second trial. Among them, 74 employees participated in both surveys and were matched. Participation in the two surveys was anonymous and the participants were asked to complete three questionnaires. Results : The intervention was not effective in reducing perceived poor health, accidents, hospitalizations, sick leaves, medication use, musculoskeletal disorders, psychosocial distress and job stress. However, there was a significant decrease in iso-strain and an increase in social support. Iso-strain decreased, especially among women (p < 0.002) and employees (p < 0.001). The increased support provided by supervisors and colleagues benefited women and employees, while improved emotional support from supervisors and colleagues mainly benefited employees. These trends were associated with psychological and musculoskeletal disorders. Conclusions : The significant decrease of iso-strain through improved social support suggests that efforts to prevent work-related stress need to be pursued.