Genetically modified mice were first reported in 1980–81 by five different labs working independently in the USA and Europe, in diverse disciplinary contexts. What these groups had in common was a combination of expertise and practical experience in molecular biology, especially the new methods of detecting recombinant DNA, and the developmental biology of the mouse. All of them also had access to the growing network of academic centres where new genes were being isolated, purified and introduced into different cells. These ‘transgenic’ mice were thus made possible by networks of academic researchers sharing materials, results and techniques. The moral economies of sharing biological materials and exchanging techniques have been explored as a key aspect in the history model organism communities, especially at the time of their making. In the 1970s, the changes in the politics of science had a significant impact on the experimental and communicative practices of biological research. The debates and regulation surrounding recombinant DNA affected experimental programmes and limited the sites where they could be pursued. Heightened media attention to molecular biology made the day-to-day practices of the laboratory visible, and encouraged more scientists to engage with broader audiences. The increasingly important role of commercial interests and research sites affected the politics of sharing resources and information, but also expanded the permissible arenas for announcing discoveries. The expansion of molecular biology to higher organisms and the concurrent molecularisation of developmental biology have been considered by some scholars, but much remains to be understood. This paper places developmental biologists, geneticists and molecular biologists who tried to introduce foreign genes into whole mice in the context of biomedical research of the late 1970s. It explores how different scientists, most of them in well-funded and established groups, engaged with the expanding field of recombinant DNA research and adapted its practices and agendas to their work, before the cutting-edge tools it required were widely disseminated or standardised.