Since the early 1990s, health care information companies have bought electronic records of prescriptions from pharmacies and other sources and linked them with information about doctors that is licensed from the Physician Masterfile of the American Medical Association (AMA). These information companies, the largest of which is IMS Health of Fairfield, Connecticut, have then compiled and sold individual physicians' prescribing data to pharmaceutical manufacturers. The business is lucrative. But a growing number of physicians have rebelled after becoming aware that drug companies have access to their data — in some cases because zealous sales agents have confronted them with their prescribing histories.1 The abuses have occurred despite “best practice guidelines” from the AMA that include admonitions that industry and its representatives should keep prescribing data confidential, that companies should prohibit disclosure “by sales representatives to any other party,” and that “the use of prescribing data to overtly pressure or coerce physicians to prescribe a particular drug is absolutely an inappropriate use.”