In Three Contributions to the Theory of Sex, Freud followed the lead of Krafft-Ebing in applying the concept of bisexuality to the central as well as to the peripheral parts of sexual functioning. This concept, formulated as a general characteristic of every human individual, came to play so important a rôle in psychoanalytic theory that younger men dealt with it not as a postulate or convenient frame of reference for interpretation, but as an established fact. Freud in 1933 reiterated that he had merely 'carried over the notion of bisexuality into mental life'. Verification of this hypothesis rests with biology. The