ABSTRACT Objective: To describe how local research ethics committees (LRECs) consider and apply research ethics in the evaluation of biomedical research proposals. Design: A qualitative study was conducted using purposeful sampling, focus groups and a grounded theory approach to generate data and to analyse the work of the LRECs. Setting and participants: 11 LRECs of the Mexican Institute of Social Security (IMSS). Results: LRECs considered ethics to be implicit in all types of research, but that ethics reviews were only necessary (...) for projects that included the direct participation of human beings. The LRECs appeared to understand the importance of consent, as in the completion of a consent form, but did not emphasise the importance of the process of acquiring ‘informed’ consent. The committees considered their main roles or functions to be: (a) to improve the methodological quality of research and to verify – if applicable – the ethical aspects; (b) to encourage personnel to undergo research training; (c) to follow‐up research to oversee the adherence to norms and compliance with a specified research timetable. Conclusions: This study provides a valuable insight into how these LRECs understand the ethical review process. The emphasis of the committees was on rules, regulations, improving research methodology and research training, rather than a focus on efforts to protect the rights and well being of research subjects. The results encourage further normative and descriptive lines of investigation concerning education and the development of LRECs. (shrink)