This article discusses how sensitive bioethical issues are addressed in legislation, using as a starting point the analysis of a corpus of normative texts relating to Assisted Reproduction Technologies (ARTs), and in particular surrogacy, enacted in various English-speaking countries. In the investigation, special special attention is given to the re-elaboration and presentation of scientific knowledge in legal discourse with a view to detecting any possible slant or changes, and the reasons thereof. Another important object of investigation is the redefinition of certain well established categories of kinship because of the disruptive effects of biomediacal advances, and ARTs in particular, on family-based social relations. The analysis will focus on legal definitions, which are crucial in this domain considering that advances in the modern technosciences have brought about the need to categorize and name new medical practices and the situations they contribute to bringing about. The focus will be on how definitions are used in normative texts, functioning as initiators of a dynamic process generating discourses that acquire their meaning in the social and communicative contexts they are embedded in. Special attention will be devoted to the way in which specialised scientific, and especially medical, terminology and concepts, are dealt with in bioethically relevant legal discourse.