Traditionally, in the industrial field, the workers’ expertise in their own jobs does not figure in production organization. However, when the changes that work teams bring to their prescribed tasks in order to carry them out more efficiently are not taken into account, or when “top-down” management is imposed on cooperation between workers, the implicit work that this cooperation requires is devalued, and health problems appear. The investigation which we will present supports just such an interpretation of the genesis of health problems observed among workers on an electronics factory production line after the reorganization of their workshop. We will then describe the new dynamic that opened up via a debate within the work team itself as to what cooperation really means. The debate was grounded in the participants examining their own and then their colleagues’ actions, a method put forward within this study by researchers from the “Clinic of activity” team of the CNAM (Centre de Recherche, Travail et Développement – CRTD).