In 1947 the Medical Research Council of Britain established the Laboratory Animals Bureau in order to develop national standards of animal production that would enable commercial producers better to provide for the needs of laboratory animal users. Under the directorship of William Lane-Petter, the bureau expanded well beyond this remit, pioneering a new discipline of "laboratory animal science" and becoming internationally known as a producer of pathogenically and genetically standardized laboratory animals. The work of this organization, later renamed the Laboratory Animals Centre, and of Lane-Petter did much to systematize worldwide standards for laboratory animal production and provision-for example, by prompting the formation of the International Committee on Laboratory Animals. This essay reconstructs how the bureau became an internationally recognized center of expertise and argues that standardization discourses within science are inherently internationalizing. It traces the dynamic co-constitution of standard laboratory animals alongside that of the identities of the users, producers, and regulators of laboratory animals. This process is shown to have brought into being a transnational community with shared conceptual understandings and material practices grounded in the materiality of the laboratory animal, conceived as an instrumental technology. © 2010 by The History of Science Society.