Definition of the problem The creation and selection of children as tissue donors is ethically controversial. Critics often appeal to Kant’s Formula of Humanity, i.e. the requirement that people be treated not merely as means but as ends in themselves. As many defenders of the procedure point out, these appeals usually do not explain the sense of the requirement and hence remain obscure. Arguments This article proposes an interpretation of Kant’s principle, and it proposes that two different instrumental stances be (...) distinguished. I argue that the creation of “saviour children” is a form of instrumentalization that I dub “preemptive instrumentalization” and that it is categorically different from earlier forms of instrumental attitudes concerning human reproduction. Conclusion Critics are wrong to claim that Kant’s principle is either compatible with the selection of saviour siblings or too vague to serve as an ethical principle. (shrink)