The evolution of Western medicine since World War II has resulted in the emergence of new practices based on the direct interaction of biology and medicine. The post-war realignment of biology and medicine has been accompanied by the emergence of a new type of objectivity, regulatory objectivity, that is based on the systematic recourse to the collective production of evidence. Unlike forms of objectivity that emerged in earlier eras, regulatory objectivity consistently results in the production of conventions, sometimes tacit and unintentional but most often arrived at through concerted programs of action. These actions incorporate unprecedented levels of reflexivity, in the sense that biomedical practitioners in their debates and discussions take into account the conventional dimension of their endeavors. The conventions produced by regulatory objectivity create the conditions for a clinical objectivity that relies on the existence of entities and protocols produced and maintained far outside the intimate encounter between doctor and patient. By establishing endogenous forms of regulation, regulatory objectivity operates on a different plane and in a different mode from those suggested by analysts who treat all regulation as a form of rationalization imposed upon medicine from without.