New forms of life produced by biomedical research, such as human embryonic stem cells (hESC), have been the object of public debate beyond the scientific fields involved. This article brings to light the case of Brazil, where recently passed federal legislation has authorized research with in vitro human embryos. It focuses on the legislative debate in the Brazilian National Congress between 2003 and 2005 on the Biosafety Bill of Law, which cleared for hESC research a certain share of supernumerary and unviable human embryos frozen in the country's assisted reproduction clinics. The passing of this Bill triggered other public reactions, chiefly a Direct Action of Unconstitutionality in Brazil's Federal Supreme Court. This study adopts an anthropological perspective for describing and analyzing the chief arguments in both debates, in terms of how the notion of 'life' was deployed and negotiated by contending parties. If, on the one hand, the definition of life appeared firmly attached to a conception of both the in vitro embryo and the fetus as a human person, on the other a movement towards breaking down life along utilitarian lines was found when the potential beneficiaries of stem cell therapy came into the equation. In all cases, however, notions of life were negotiated from a hybrid continuum of (biological) facts and (religious, moral and juridical) values, and resonated in different ways with the idea of the individual as privileged mode of constructing personhood in the context of modern nation states.