This article addresses the use of sexual relations with research informants in fieldwork for the purpose of gathering information. The analysis is based on the research that the author himself carried out between 2009 and 2014 on anonymous sexual encounters between men in public places in Catalonia. The article aims to demonstrate that sexual interaction with informants - notwithstanding appeals to scientific objectivity and professional ethics - can be a useful tool for gaining a better understanding of social reality. This study on anonymous sex shows that participating in sexual activity can provide the researcher with a great deal of information which would not be accessible via other relationships with research informants. However, the article also addresses certain limitations - which cannot be ignored - in fieldwork of this sort and in the interpretation of the data obtained.