A growing number of doctors in the United States are joining online professional networks that cater exclusively to licensed physicians. The most popular are Sermo, with more than 135,000 members, and Doximity, with more than 100,000. Both companies claim to offer a valuable service by enabling doctors to "connect" in a secure online environment. But their business models raise ethical concerns. The sites generate revenue by selling access to their large networks of physician-users to clients that include global pharmaceutical companies, market research and consulting firms, and hedge funds and other investors. In exchange for a fee, these clients are offered a variety of tools to monitor, analyze, and solicit physicians' opinions. In Sermo's case, clients are also offered opportunities to conduct "awareness campaigns" on the site that are aimed at influencing physician sentiment about specific drugs and medical devices. In effect, these online networks have created an even more efficient means for the pharmaceutical industry to track physician sentiment, disseminate messages, and cultivate key opinion leaders. This paper argues that the dual nature of these sites (a) undermines their integrity and transparency as forums for the exchange of medical opinion and (b) presents an ethical conflict for the doctors who use them.