 Limits on risks are a central part of almost all current research regulations and guidelines. With respect to those who can consent, there is an essentially implicit agreement that the risks should not be too high (as noted earlier, some argue that there should not be any net risks to even competent adults in the context of so-called therapeutic research). However, there is no consensus regarding how to determine which risks are acceptable in this context. With respect to those who cannot consent, many commentators argue that clinical research is acceptable when the net risks are very low. The challenge, currently faced by many in clinical research, is to identify a standard, and find a reliable way to implement it, for what constitutes a sufficiently low risk in this context. An interesting and important question in this regard is whether the level of acceptable risks varies depending on the particular class of individuals who cannot consent. Is the level of acceptable risks the same for individuals who were once competent, such as previously competent adults with Alzheimer disease, individuals who are not now but are expected to become competent, such as healthy children, and individuals who are not now and likely never will be competent, such as individuals born with severe cognitive disabilities?