The history of research on the association between platelet monoamine oxidase 
(MAO) activity and personality traits, such as sensation seeking and 
impulsiveness, is reviewed. The effects of MAO-inhibiting compounds in cigarette 
smoke for the interpretation of this association are discussed. Recent results 
confirming a true association between platelet MAO activity and personality are 
presented. From a clinical point of view, this association has had its greatest 
impact on the understanding of the nature of constitutional factors making 
individuals vulnerable for e.g. substance abuse and the link between low 
platelet MAO activity and type 2 alcoholism, recently confirmed on non-human 
primates, is discussed. The molecular mechanisms underlying the association 
between platelet MAO and behaviour are discussed and evidence that common 
transcriptional factors, e.g. within the AP-2 family, regulating both the 
expression of platelet MAO and components of central monoaminergic systems, such 
as synthetizing enzymes, receptors and transporters, are presented. A hypothesis 
is put forward, that such common transcription factors may not directly regulate 
platelet MAO expression, but rather mitochondrial number or outer membrane 
surface.