This paper analyses the complex issues faced by regulators of the infertility treatment industry in response to the social and technological changes that heralded a new openness in knowledge about genetics, paternity and the concomitant need for donor offspring to know their genetic origins. The imperative for full information about their donor and biological father, who contributed to their creation and half of their genome, was an outcome unanticipated by the architects of the donor insemination programme. Genetic paternity testing realised (...) the possibility of fixed and certain knowledge about paternity. This paper outlines medicine's role in the formation of normative families through the use of donor insemination. Extending information from an Australian study on the use of DNA paternity testing, it analyses what the social and scientific changes that have emerged and gained currency in the last several decades mean for the new ‘openness’ and the role of paternity testing in this context. It concludes with recommendations about how to deal with the verification of paternity in linking donor conceived adult children to their donor. (shrink)