Bisexuality is arguably Freud's most overdetermined foundational concept and also the one that has received the least critical attention. The author employs the Lacanian notion of primacy of the signifier to critique psychoanalytic representations of bisexuality as a primordial, undifferentiated state; she suggests that what is in fact primordial and undifferentiated is the signifier itself. Insights from the history of science and feminist theory are used in critically examining the primordial signifier of bisexuality. The author likewise raises the question of the psychoanalytic community's motivations for retaining this signifier.