The debate concerning the moral permissibility of using human embryos in human embryonic stem cell (hESC) research has long centred on the question of the embryo's supposed right to life. However, in focussing only on this question, many opponents to hESC research have escaped rigorous scrutiny by making vague and unfounded appeals to the concept of moral respect in order to justify their opposition to certain hESC practices. In this paper, I offer a critical analysis of the concept of moral respect, and its use to support the intuitively appealing principle of proportionality in hESC research. I argue that if proponents of this principle are to justify its adoption by appealing to the concept of moral respect, they must explain two things concerning the nature of the moral respect owed to embryos. First, they must explain which particular aspect of the embryo is morally relevant, and why. Second, they must explain why some uses of embryos in research fail to acknowledge what is morally relevant about the embryo, and thereby involve a violation of the moral respect that they are due. I shall show that providing such explanations may be more difficult than it first appears.