: The "difference position" holds that clinical research and therapeutic medical practice are sufficiently distinct activities to require different ethical rules and principles. The "similarity position" holds instead that clinical investigators ought to be bound by the same fundamental principles that govern therapeutic medicine—specifically, a duty to provide the optimal therapeutic benefit to each patient or subject. Some defenders of the similarity position defend it because of the overlap between the role of attending physician and the role of investigator in (...) a research trial. This overlap is maximal when the same physician occupies both roles with respect to a particular patient-subject. We address the ethical tensions inherent in that role conflict and argue that the tensions are real but manageable. The difference position provides a sound ethical framework within which to manage those tensions, while the similarity position is unsatisfactory because it seeks to deny the existence of the tensions. (shrink)