Paper presented at 2009 JSWEC Conference. The implementation of the Mental Capacity Act 2005 has implications for social researchers as well as health and medical research. The Act, however, is focused on the latter and Ethics Review for social research, where people may lack decision-making capacity to take part, presents complexities that have not yet been fully addressed. This paper reports a study of social work researchers’ involvement in university research ethics committees where the capacity of participants may be an issue. The findings suggest that perceived implications of the Act may inadvertently stifle important research and, if not carefully negotiated, the use of Research Ethics Review may prevent rather than enable people to become involved in research as participants. This may infringe the rights of people to participate in research and, therefore, may detract from the principles of the Act in presuming and enabling capacity where possible. The research was undertaken in two stages. A web-based search and documentary analysis of a sample of university research ethics committees’ policies and procedures determined current practice. The second stage involved semi-structured interviews with social work/social care researchers likely to be involved in areas covered by the Act. These interviews were thematically analysed to explore how ethical issues were considered, whether explicit account was taken of the Mental Capacity Act and in what ways the Act was believed potentially to impact on future research proposals. The study suggests there has been little attention to the implications of the Act so far by social work researchers, but where it has been considered problems have been identified. This paper makes some suggestions for negotiating university research ethics committees and making positive use of the Mental Capacity Act in developing research proposals where capacity may be an issue.