The availability of embryonic stem (ES) cells isolated from human blastocysts may open novel avenues for medical treatment of otherwise incurable diseases. Yet the generation of human ES cells requires the destruction of early human embryos. This confronts us with the moral problem of whether it is justifiable to sacrifice human life in order to treat other human life. This article outlines the development of the German debate about research with ES cells and explicates the arguments that are central to that debate with respect to the aims and means of research with ES cells. With regard to the means, the isolation of ES cells from human embryos raises the question of the moral status of the human embryo. A restrictive position acknowledges the human dignity of the embryo in its very early stage of development and claims that the embryo's life must be protected accordingly. In contrast, a gradualist position acknowledges human dignity, and therefore the full level of protection, only when the embryo has reached a certain stage of development. In addition, the intentions behind the generation of human embryos, i.e. exclusively for research purposes, and the mode of generating them, i.e. by nuclear transfer technology, have strong ethical relevance in the German debate. Based on these results, the ethical reasoning underlying the draft of a Stem Cell Act recently passed by the German Parliament is outlined.