In The Case for Animal Rights, Tom Regan argues that, in addition to the negative duty not to harm nonhuman animals, moral agents have a positive duty to assist nonhuman animals who are victims of injustice. This claim is not unproblematic because, in many cases, assisting a victim of injustice requires that we harm some other nonhuman animal(s). For instance, in order to feed victims of injustice who are obligate carnivores, we must kill some other animal(s). It seems, then, that (...) sometimes the duty to assist nonhuman animals who are victims of injustice conflicts with the prima facie duty not to harm nonhuman animals. In defense of Regan’s theory against this apparent inconsistency, I introduce an additional principle, the “guardianship principle,” which can be used to illustrate how we can be justified, under certain conditions, in overriding our prima facie duty not to harm nonhuman animals in order to fulfill our duty to assist nonhuman animals who are victims of injustice. (shrink)