In this brief paper I intend to make some distinctions between the activities that research ethics committees are required to undertake as part of their role in protecting research participants. These functions are, identifying ethical issues and risks within research projects, providing advice on how to resolve these issues and risks without compromising the validity of the research and finally, when this cannot be achieved, deciding whether the research should still be allowed to go ahead. Distinguishing these distinct functions allows (...) us to determine what an appropriate membership of a Research Ethics Committee is. I will sketch out the implications of these functions for the appropriate membership of NHS and university based ethics committees in the UK. (shrink)