In this article we introduce the notion of entrenchment to conceptualize the processes in which new technological options, through the interactions between a variety of actors, become viable and established practices in society, both satisfying and modifying needs and interests. The notion of entrenchment we use as a framework for an analysis of developments and debates in the field of cystic fibrosis testing and screening in Denmark. On the one hand, it appears that the development and introduction of cystic fibrosis (CF) screening to some extent is predetermined both by existing networks of human genome researchers, clinical geneticists, patients (organizations), funding organizations, and regulatory agencies, and by existing practices like that of prenatal diagnosis. On the other hand, in Denmark, the content and future of CF screening is shaped in ongoing processes or articulation of demand for screening and of its cultural and political acceptability, processes which also involve political decision-making and which (may) result in new networks and regimes. Yet, what appears to be an inherent and undecided part of the process of entrenchment of CF screening in Denmark, is how to allocate responsibilities and authority to decide what is acceptable and what not.