The aim of this study is to investigate the possible link between Shoham's personality-core theory [1] and addiction to hard drugs. Basing ourselves on Kleinean premises, that the oral stage is critical in the formation of behavioural patterns, which are influential throughout life, we hypothesize that in the oral stage two opposing vectors, 'separation' and 'participation' are initiated. By 'participation' we refer to the identification of ego with an external object or symbol, and continuous tendency to lose the personal identity by fusion with this object or symbol. 'Separation' is the opposite vector and expresses ego's tendency to incorporate the external object or symbol. These vectors form two multidimensional personality axes, on which the different personality types and behavioral patterns can be anchored. This study aims at investigating the connection between these two vectors and drug addiction. We view drug addiction as a functional behaviour pattern, which brings the individual to a state of internal balance. Shoham's personality theory hypothesizes the derivation of behavioural patterns of different personality 'types', according to the strength of the two vector - the 'separant' and 'participant' types. It is hypothesized that the drug use and the experience gained by using the specific drug by different personality types will vary according to the prominence of the core personality vector. The potency of these vectors is related to an early oral (participant) or a later oral (separant) fixation.(ABSTRACT TRUNCATED AT 250 WORDS)