This communication presents a participatory diagnosis on discrimination carried out between 2007 and 2009 for an Argentine non-governmental organization (Association for Civil Rights – ADC). The diagnosis dealt with various national, ethnic and religious collectives from Greater Buenos Aires in whose construction migration is or has been a “marking” factor (Bolivian and Korean immigration, refugees, Rom people, Arab and Jewish communities). The study aimed to explore situations and patterns of discrimination, discrimination perceptions and collective actions against it. In order for the diagnosis to grasp different and divergent “community” voices, research and case- compilation activities were undertaken jointly with referents of the selected groups. The participatory approach adopted poses questions and challenges that deserve to be reflected upon. Therefore, the presentation of the diagnosis is conveyed in a double key: the exhibition of some of its outputs, and the narrative account of its methodological design and development.