This paper discusses how the American public accounts for the concerns that they have about genetic research and the benefits that they foresee. We develop a general framework for discussing public claims about genetic technology based on Stephen Toulmin's model of warrants in argumentation. After a review of the results from public opinion polls about genetic research, we present a focus group study of public understandings of genetics. We outline the warrants, or publicly accepted "good reasons", that this group offers for accepting some aspects of genetic technology and for rejecting other aspects. The warrants presented by the public in their discussion of genetic research indicate that the public has a complex, informed understanding of genetic research, albeit a non-technical one. The paper concludes with a discussion of the importance of public participation in debates over genetic research and the ways that researchers and policymakers could adapt to public concerns about genetics.