In November 2004, the Swiss population voted to accept a law on research using human embryonic stem cells. In this paper, we use Switzerland as a case study of the shaping of the ostensibly ethical debate on the use of embryos in embryonic stem cell research by legal, political and social constraints. We describe how the national and international context affected the content and wording of the law. We discuss the consequences of the revised law's separation of stem cell research from other forms of embryo research, its definitions of embryo and of spare embryos, and the introduction of donorship into the Swiss ethical debate on IVF. We focus on the exclusion of the potential embryo donors' voices and perspectives from the debate, and consider the effects of this exclusion on ethical discourse and the political process.