The Select Agent Program was one of the US government’s legal responses to the mail anthrax attacks in 2001 and to the perceived risks associated with recent developments in synthetic biology. A “select agent” is a microorganism or a toxin whose handling, transportation, and storage are controlled by federal laws. Since its inception, this regulatory framework has fostered opposition from biomedical researchers, partly because of its time-consuming features. As I argue here, however, grounds for resistance have also turned on whether there is anything specific to so-called “pathogenic organisms” that warrants their being classified as select agents. For, while providing a more complex picture of the microbial world, current dynamical perspectives on host-parasite interactions operate as a platform from which to criticize taxonomic lists of select agents. One such perspective, the damage-response framework, developed by immunologist and biosecurity expert Arturo Casadevall, reconceptualises host-agent interactions by situating pathogenicity on a continuum, rather than locating it in a specific structure of either the host or the parasite. This paper illustrates how the damage-response framework provides arguments for rejecting the Select Agent Program, often charged for being blind to biological variation as well as to the context-sensitive nature of infectious diseases and further explores how the threats of naturally emerging diseases and bioterrorism are intertwined by scientists intending to rationalize a relaxation of regulations. Finally, a discussion of the different forms of regulation relevant in this context is introduced. More generally, this article calls attention to ways in which biomedical concepts circulate between science and science policy, and how they shape scientific practices along the way.