The use of brain imaging technology as a common tool of research has spawned concern and debate over how investigators should respond to incidental findings discovered in the course of research. In this article, we argue that investigators have an obligation to respond to incidental findings in view of their entering into a professional relationship with research participants in which they are granted privileged access to private information with potential relevance to participants' health. We discuss the scope and limits of this professional obligation to respond to incidental findings, bearing in mind that the relationship between investigators and research participants differs fundamentally from the doctor-patient relationship.