In this paper, I motivate skepticism about the causal efficacy of moral properties in two ways. First, I highlight a tension that arises between two claims that moral realists may want to accept. The first claim is that physically indistinguishable things do not differ in any causally efficacious respect. The second claim is that physically indistinguishable things that differ in certain historical respects have different moral properties. The tension arises to the extent to which these different moral properties are supposed (...) to have different effects on people. I will introduce a class of cases in which this tension arises and suggest that the moral properties in these cases have no causal power. I will also question whether there are differences between the moral properties in these cases and moral properties in other cases that do not involve physically indistinguishable things that could make the latter moral properties causally efficacious. The second way that I motivate skepticism consists in pointing out a unique feature of cases in which moral properties are supposed both to supervene on historical properties and to be causally efficacious. These cases allow us to change moral properties with alleged effects while we hold constant the nonmoral candidates for causal contribution to those effects. This feature of these cases is unique because in most other cases the moral properties supervene on the physical properties in the nonmoral candidates, such that we cannot change the former while holding constant the latter. This way of changing moral properties provides empirical grounds for testing their causal efficacy. (shrink)