This paper describes a three-year project designed to build the capacity of members of research ethics committes to perform their roles and responsibilities efficiently and effectively. The project participants were made up of a cross-section of the membership of 13 Research Ethics Committees (RECs) functioning in Nigeria. They received training to develop their capacity to evaluate research protocols, monitor trial implementation, provide constructive input to trial staff, and assess the trial's success in promoting community engagement in the research. Following the (...) training, technical assistance was provided to participants on an ongoing basis and the project's impacts were assessed quantitatively and qualitatively. Results indicate that sustained investment in capacity building efforts (including training, ongoing technical assistance, and the provision of multiple tools) improved the participants’ knowledge of both the ethical principles relevant to biomedical research and how effective REC should function. Such investment was also shown to have a positive impact on the knowledge levels of other RECs members (those who did not receive training) and the overall operations of the RECs to which the participants belonged. Building the capacity of REC members to fulfill their roles effectively requires sustained effort and investment and pays off by enabling RECs to fulfill their essential mission of ensuring that trials are conducted safely and ethically. (shrink)