The governance of front-line professionals is a persistent organizational problem. Regulations designed to make professional work more legible and responsive to both organizational and public expectations depend on these professionals’ willing implementation. This paper examines the important question of how professional control shapes regulatory compliance. Drawing on a seventeen-month ethnographic study of a bioscience laboratory, we show how professionals deploy their discretionary judgment to assemble environmental, health, and safety regulations with their own expert practices, explaining frequently observed differential rates of regulatory compliance. We find that professional scientists selectively implement and blend formal regulations with expert practice to respond to risks the law acknowledges (to workers’ bodies and the environment) and to risks the law does not acknowledge but professionals recognize as critical (to work tasks and collegiality). Some regulations are followed absolutely, others are adapted on a case-by-case basis; in other instances, new practices are produced to control threats not addressed by regulations. Such selective compliance, adaptation and invention enact professional expertise: interpretations of hazard and risk. The discretionary enactment of regulations, at a distance from formal agents, becomes part of the technical, practical, and tacit assemblage of situated practices. Thus, paradoxically, professional expert control is maintained and sometimes enhanced as professionals blend externally imposed regulations with expert practices. In essence, regulation is co-opted in the service of professional control. This research contributes to studies of professional expertise, the legal governance of professionals in organizations, regulatory compliance, and safety cultures.