In the aftermath of the 2009 outbreak of H1N1 influenza, scientists in Mexico sought to develop bioseguridad, that is, to protect biological life in Mexico by safely conducting research on infectious disease. Drawing on ethnographic research in laboratories and with scientists in Mexico, I look at how scientists make claims about local differences in regulations, infrastructure, bodies, and culture. The scientists working with infectious microbes sought to establish how different microbial ecologies, human immune systems, and political and regulatory systems made the risks of research different in Mexico from other countries. In developing bioseguridad, the idea of globalized biology that animates many public health projects was undermined as scientists attended to the elements of place that affected human health and safety. Scientists argued for the importance of local biologies, generating tension with global public health projects and regulations premised on the universality of biology.