In order to explore practitioners' motivations to participate in epidemiological research, a study was conducted among doctors who had been requested to provide clinical information on their patients included in the group study DESIR in the Inde and Loire regions of France. Six semi-structured individual interviews were carried out by two sociologists, and were then followed-up by 216 questionnaires, 80 of which were completed and analysed. Finally, 18 telephone interviews were conducted to complete the data collected. Reasons given for participating in epidemiological studies are mainly the perceived scientific interest, relevance for public health and the feeling of being a partner in the research. The obstacles seem to be the vague image of the promoter, ignorance of the DESIR study's objectives, lack of direct contact for communicating information, and the mixture and confusion between filling out the study's questionnaire and handling administrative constraints in general. Therefore, better communication, centred on the concept of partnership between research and practical medicine, informing on the usefulness of knowledge from epidemiological studies for the practice of medicine, and clarifying the promoter's role, could improve the level of participation from general practitioners.