The subject of the study is the analysis of two arguments that have appeared in the Czech-Slovak philosophical setting in the context of discussions about the moral evaluation of research into stem cells of human embryos. We have presented various reasons (varied understandings of potentiality and the vagueness of the expression “living human body”), on the basis of which we must reject the argument of P. Volek concerning the unconditional protection of each human zygote. With respect to the argument of A. Doležal, D. Černý a T. Doležal, we have shown that their critique of the conception of non-individuality of the early human embryo relies on the identification of the concept of the “individual” with the concept “particular” which, for ontological reasons, cannot be accepted. In both of the analysed bioethical arguments the key role of metaphysical concepts and conceptions is easily demonstrated., Peter Sýkora., and Obsahuje poznámky a bibliografii