Recent work in science and technology studies has looked at how chemical industries manufacture doubt about the toxicity of their products and manage to establish their scientific views in the field of international regulations on toxic substances. Rather than examining yet another “victory” for the industry, this article analyzes the deployment of a “pro-industrial” scientific position, punctuated mainly by failure and opposition. This trajectory is tracked through the analysis of several data sets: archives, scientific documentation, and sociological interviews. The first part of the article charts the development of a biochemical concept, “peroxisome proliferation,” within an academic subfield and its subsequent appropriation by certain industrial parties who used it as a defensive weapon for their commercial interests. Through the example of the International Agency for Research on Cancer and its network of interdependent institutions, the article goes on to analyze the multiple attempts of chemical industry players to establish their interpretation of the concept within the regulatory bodies for carcinogenic substances. The study of such systems of sociological interdependence shows that a full analysis of the “doubt manufacturing” requires an examination not only of the manufacturing process but also of the reception of the ideas produced.