This article illustrates the differences between expert assessment procedures in France and the United States by comparing their respective procedures for the risks raised by perchlorate, an environmental contaminant detected in drinking water and food. This example highlights the contrast between the two models, one based on confrontation and stakeholder involvement, the other on consensus and the centralization of experience. The main differences lie in the way interactions between the various bodies responsible for the assessments and the other stakeholders are formalized, in the procedures governing audits of the risk assessments, and in the role of researchers in the production of these assessments. After describing the differences, the article describes the advantages and drawbacks of the two systems and concludes with a proposal for the development of an intermediate method for EU institutional expert appraisals, combining a centralizing approach with pluralist and collegial principles.