Despite its several variations, the central position of equipoise is that subjects in clinical experiments should not be randomized to conditions when others believe that better alternatives exist. This position has been challenged over issues of which group in the medical or research community is authorized to make that determination, and it has been argued that informed consent provides sufficient ethical protection for participants independent of equipoise. In this paper I frame ethical participation in clinical research as a two-party decision (...) process involving offering and accepting participation under informed consent. Nine conditions are identified in which it is possible that potential participants and researchers or care professionals can rationally choose divergent actions based on identical understandings of the situation. Under such circumstances, researchers or care professionals cannot ethically substitute their understanding of equipoise in the situation for the patients’ choices, or vice versa. (shrink)