As a biomedical boundary marker, the distinction between treatment and enhancement has been enshrined in policies at both professional and governmental levels, and continues to inform much of the public discussion of new biomedical advances. However, this distinction is explicated in several different ways, which have different merits as boundary markers for biomedical research and practice. In fact, with philosophical scrutiny, the distinction often seems in danger of collapsing entirely under conceptual critiques even before the question of its moral merits is entertained.