BACKGROUND Non-participation of general practitioners (GPs) is a serious source of bias for practice-based studies. Objective. To elucidate doctors' motives for non-participation in, and subjective barriers to, general practice research. METHODS German GPs that had opted out of a quality assessment project involving electronic patient records (EPRs) were mailed a questionnaire regarding their attitudes towards general practice research and their specific objections to the current project. A sub-sample of doctors was interviewed. Their statements were coded and classified with regard to the reasons given for non-participation and possible motivating factors. RESULTS The survey response rate was 37% (96/263); 21 GPs completed an additional qualitative interview. Nearly all respondents (88/96) considered general practice research to be important, but 58% had not previously participated in research projects and 56% would not do so in the future. Nearly half (47/96) were opposed to having data extracted from their EPRs. The qualitative analysis revealed deep concerns related to the collection of EPRs (e.g. potential misuse of data, being subject to control or resulting computer problems). Some GPs expressed concerns about recruiting their own patients for the study. Some doctors complained of not being sufficiently recognized as a partner or not having a voice in the research process. CONCLUSION Doctors' negative attitudes, concerns and ambivalent feelings should be addressed in recruitment strategies, especially when the analysis of EPRs or direct patient contact is required. Some doctors do not participate in research out of principle and will be very difficult to convince.