[The other side of the fence. When the world of mental health and street meet research].

Considering the patient as a partner or a collaborator is becoming more and more popular in the field of mental health research. Nevertheless, relational dynamics between patients and researchers and the issues raised by them aren't much studied. This article aims to open the debate from a case study: the participation of a peer worker to two research teams of a research and demonstration project in the field of mental health and homelessness. The story of his experience in the project explores how the realities that affects him--at the intersection of mental health problems, experience in the street and the world of consumption--have an impact on his relationships with his colleagues. Conversely, his working conditions seem to negatively affect him and produce a certain loss of identity leading him, among other things, to leave the project. The analysis suggests that conflicts that arise between the peer and his colleagues reflect hierarchies between social status and legitimate knowledge (or that needs to be recognized as valid) in the field of research.