Xenotransplantation is an example of a developing biotechnology which highlights three differing interests in the health of the public; a specific interest in enhancing the health of individuals who require a particular procedure or treatment, a wider interest in protecting the health of us all by avoiding introducing biotechnologies which risk the health of the public, and a public interest in advancing medical knowledge and treatment. Here we explore how matters of private benefit and public risk can be appropriately reconciled and consider whether ideas of public health should take a more central role when deciding whether clinical xenotransplantation should proceed. The risks of xenotransplantation are not certain but the nature of the harm to individual and public health could be severe. The concept of risk is central to our analysis as xenotransplantation threatens potential future harm as well as possible benefit. We argue that it is sometimes legally and ethically necessary for the state to act in advance to protect the health of the public, and that xenotransplantation is such a case. In reaching this conclusion we adopt a precautionary approach; an approach which we modify by Mill’s harm principle.