A remarkable decision of the General Court of the European Union deals with the regulatory requirements that to be met by scientific knowledge in order to justify the non-renewal of an authorization by the European Commission for plant protection products. The following essay takes this as an opportunity, in the sense of a case study, to present and explain the structures of European chemicals law along which scientific risk knowledge is processed. The case study demonstrates how the delicate mechanisms of knowledge generation and knowledge processing in European chemicals law, balanced by differentiation of organization and procedures, work as regulatory practice under judicial review. Risk assessment does not stop at formal criteria, but is also based on substantive requirements that follow legal rules and are controlled by the European jurisdiction. The research has shown that behind the semantics of administrative discretion lies a robust control regime designed to ensure appropriate standards of rationality of administrative assessments.