In general, the literautre review provides theoretical explanations for the popular, common-sense belief that a little stress improves performance, whereas when stress becomes severe, performance declines and ultimately breaks down. In terms of psychological stress (as opposed to physiological) the single most important variable appears to be the subject's interpretation of the stress-producing stimuli. Increases in adrenaline and noradrenaline accompany a variety of emotional responses, but differential proportions are not seen as characterizing the various emotions. Noradrenaline secretion appears to be related to physiological stress, or the amount of work attempted by the organism. Adrenaline secretion seems to be more-directly related to mental stress and emotional response. As emotional involvement increases, adrenal medullary secretion of adrenaline increases. The accompanying physiological and metabolic responses faciltate performance to a point; however, extremely high levels of arousal may adversely affect the athlete's proficiency. This is expecially true of sport skills requiring steadiness, precision, and concentration. Finally, for the sake of perspective, it should be stated that any contribution or complication created by the catecholamines is minimal when the entire ability range of competitors is considered. Whereas near superhuman feats by ordinary individuals caught in life-threatening situations have been reported, variations of great magnitude are unlikely in sport. The average individual is not transformed into a world class athlete merely by "getting the adrenaline flowing." Among athletes of similar physical stature and physiological function, however, adrenaline and arousal may certainly tip the scale of performance in sport.