ABSTRACTIn response to a policy of the National Institutes of Health and requirements in the revised Common Rule, a protocol for a multisite study must be reviewed by a single institutional review board (IRB), rather than by the IRB at each study site. The goal of the single IRB approach is to increase the efficiency of IRB review of multisite research without jeopardizing protections for research subjects. Yet the extent to which these joint goals are being achieved is unclear. To better understand how single IRBs function, we recruited academic, government, and commercial single IRBs (N = 49) to participate in a study involving observation of protocol review meetings and/or interviews with their members, chairs, and administrators. Twenty (40.8%) agreed to participate, of which 50% agreed to both interviews and observation. While 81.8% (9/11) of academic and 50% (4/8) of government single IRBs participated in some way, only 23.3% (7/30) of commercial single IRBs did so. The four largest commercial single IRBs declined to participate. Because evaluation of single IRBs is important to inform development, implementation, monitoring, and refinement of federal policies, single IRBs should be encouraged to participate in research that examines how they function.