 To assess the ethics of exposing research participants to risks, one needs an account of why exposing others to risks raises ethical concern in the first place. Being exposed to risks obviously raises concern to the extent that the potential harm to which the risk refers is realized: the chance of a headache turns into an actual headache. Being exposed to risks also can lead to negative consequences as a result of the recognition that one is at risk of harm. Individuals who recognize that they face a risk may become frightened; they also may take costly or burdensome measures to protect themselves. In contrast, the literature on the ethics of clinical research implicitly assumes that being exposed to risks is not per se harmful. The mere fact that participants are exposed to risks is not regarded as necessarily contrary to their interests. It depends on whether the risk is realized in an actual harm.