Increased employee control and participation are recommended to achieve both "flexible organization" and improvements in health, as outlined in occupational stress intervention models. This study evaluates the impact of a participatory organizational intervention on job stress and job characteristics. The intervention was carried out in two post offices in the Norwegian Postal Service. "Local theories" were seen as the key drivers for organizational improvement and increased control. The underlying dynamics of the intervention were to manipulate employees' learning opportunity and decision authority so as to improve work environment and health. Work groups, in dialogue with a steering committee, conducted diagnosis, action planning, and action taking. Work conditions deteriorated during the observation period in the control groups. In one of the intervention groups, this negative trend was reduced by the intervention. Lack of positive results in the other intervention group may have been due to organizational restructuring and turbulence.