The authors studied the relationship between overachievement (defined as high school achievement in relation to intelligence) and catecholamine output (adrenaline and noradrenaline). The subjects were 176 children aged 13 yr. Adrenaline and noradrenaline excretions were measured in a neutral situation (attending a nonexciting film), and in an achievement-demanding situation. In the achievement-demanding situation, overachieving boys had much higher adrenaline excretion levels than the other boys. This difference was not found for girls. For boys, overachievement in combination with overambition (as rated by teachers) was related to a higher output of both adrenaline and noradrenaline in an achievement-demanding situation.