The use of in vitro stem cell models in toxicology represents an important opportunity to engage with the interplay of ethical and epistemological issues in regulatory science and technology. Stem cell toxicology has been proposed to tackle epistemological, ethical as well as practical problems associated with the use of laboratory animals in toxicological studies to address a shortfall in chemical risk assessments. This paper argues that these developments are problematic if viewed as simply ameliorating these problems in the near term. Stem cell toxicology arises within a relatively novel intersection of the ethics and epistemology of pluripotent stem cell research and animal experimentation. It appears to require an expansion and a diversification of ethical and regulatory oversight due to epistemological and regulatory dependencies on therapeutic stem cell biology, the entrenchment of data from animal experimentation in toxicology, and the potentially novel implications of some aspects of the research. Understanding the role of stem cell toxicology models as model for will help to grapple their role in the transfer of knowledge between non-human animal models and humans as target systems. But advancing chemical risk assessment will not be a matter of simply addressing a normative problem by scientific and technological means.