Human beings with diminished decision-making capacities are usually thought to require greater protections from the potential harms of research than fully autonomous persons. Animal subjects of research receive lesser protections than any human beings regardless of decision-making capacity. Paradoxically, however, it is precisely animals’ lack of some characteristic human capacities that is commonly invoked to justify using them for human purposes. In other words, for humans lesser capacities correspond to greater protections but for animals the opposite is true. Without explicit justification, it is not clear why or whether this should be the case. Ethics regulations guiding human subject research include principles such as respect for persons-and related duties-that are required as a matter of justice while regulations guiding animal subject research attend only to highly circumscribed considerations of welfare. Further, the regulations guiding research on animals discount any consideration of animal welfare relative to comparable human welfare. This paper explores two of the most promising justifications for these differences between the two sets of regulations. The first potential justification points to lesser moral status for animals on the basis of their lesser capacities. The second potential justification relies on a claim about the permissibility of moral partiality as found in common morality. While neither potential justification is sufficient to justify the regulatory difference as it stands, there is possible common ground between supporters of some regulatory difference and those rejecting the current difference.