In Lausanne, Switzerland, there is a growing population of migrant people of different origins. This evolving situation calls for a continuous adjustment between need and offer in terms of healthcare. Up to now, this adjustment, which involves cross-cultural adaptation processes, was based on the use of untrained interpreters. However, clinical experience shows that the use of untrained interpreters tends to keep migrant patients in an unfavourable position. This paper describes an action-research in Lausanne, which aims at the evaluation of the changes that are brought by the introduction of trained cultural mediators and interpreters (CMI) into the medical field. The paper enumerates the clinical issues that gave birth to the project and the methodological choices that were made. After discussing the first results, the authors describe how the different research stages are adapted and modified through continuous mutual influences between the field and the research process itself.