In this study, we attempt to demonstrate an association between low platelet monoamine oxidase (MAO) activity, as assessed by isotopic methods, and the stable behavioral pattern of sensation- and risk-seeking of professional bull-fighters. Sixteen professional bullfighters were studied and compared with a control group of 46 healthy control subjects who did not engage in risky jobs or activities. The group of bullfighters had significantly reduced platelet MAO activity compared with the control group (P<0.05). Bullfighters were shown to be significantly more extroverted and sensation-seeking than controls on various temperament scales. A predisposition to engage in risky activities (eg, bullfighting) and sensation-seeking could be partly conditioned by the presence of biological components of personality manifested by a significantly decreased platelet MAO activity.