In this article, I present a contractualist conception of human-participant research ethics, arguing that the most appropriate source of the rights and responsibilities of researcher and participant is the contractual understanding between them. This conception appears to explain many of the more fundamental ethical incidents of human-participant research. I argue that a system of contractual rights and responsibilities would allow a great deal of research that has often been felt to be ethically problematic, such as research involving deception, concealed research, (...) and research on dependent populations. However, in defining the conditions under which such research should be permissible, my contractualist theory also makes it clear that there are limits-and explains what those limits are-to the propriety of such research. (shrink)