We are proposing to (a) develop and refine a scale to identify individuals susceptible to the deleterious effects of stress, (b) identify the processes which underlie performance changes under stress and (c) demonstrate the usefulness of the stress susceptibility scale in an applied setting. We have previously shown that the two components of introversion/extraversion (i.e., impulsivity and sociability) behave in quite different fashions when caffeine is administered. We have also shown that these personality variables interact with time of day. We plan to (a) perform additional analyses on the personality and behavioral questionnaires to further understand these individual differences and time of day effects, (b) further investigate such task and environmental variables as time of day and degree of practice, (c) investigate additional stressors such as time pressure, task difficulty, and background noise, and (d) investigate a variety of information processing and memory tasks in an effort to determine the processes underlying these performance changes under stress. These results should prove useful in understanding and alleviating the deleterious effects of stress.