The pharmaceutical industry, in its marketing efforts, often turns to "key opinion leaders" or "KOLs" to disseminate scientific information. Drawing on the author's fieldwork, this article documents and examines the use of KOLs in pharmaceutical companies' marketing efforts. Partly due to the use of KOLs, a small number of companies with well-defined and narrow interests have inordinate influence over how medical knowledge is produced, circulated, and consumed. The issue here, as in many other cases of institutional corruption, is that a few actors have accumulated the power to shape the information on which many others base their decisions. Efforts to address this corruption should focus on correcting large imbalances in the current political economy of medical knowledge. A sequestration of pharmaceutical research and development on one hand from pharmaceutical marketing on the other, though difficult to achieve, would address this and many other problems. (© 2013 American Society of Law, Medicine & Ethics, Inc.)