This thesis explores the attempt to construct a national supply of standard laboratory- animals in Britain between 1919 and 1976. The demand for a national supply of standard laboratory-animals is located in the formation during the interwar period of the discipline of biological standardization. In contrast to other disciplines within the sciences biological standardization placed great emphasis upon the routine replication of experimental results. In consequence the field of biological standardization problematized the laboratory-animal and sought its standardization in order to construct it as a reliable diagnostic tool. In 1947 the Medical Research Council responded to pressure from an unprecedented coalition of scientific societies and established the Laboratory Animals Bureau tasked with regulating the British laboratory-animal production toward producing standard laboratory-animals. The work of the Laboratory Animal Bureau is analysed but the main focus of the thesis is upon the relationship between the practices of standardization and the promotion of the welfare of laboratory-animals. Particularly after the close of the Second World War the project to standardize laboratory-animals became increasingly associated with the promotion of their welfare. The relationship between the two was made explicit through the work of the Universities Federation for Animal Welfare in collaboration with the Laboratory Animals Bureau. In order to understand the relationship between standardization and welfare Michel Foucault's concept of biopower is employed. It is subsequently argued that the analytics of biopower need not be restricted to human life but equally encompasses non-human life. Through the Foucaultian perspective of biopower it is argued that standardization and welfare are two poles of the same biopolitical process.