The overall purpose of this investigation was to explain the acute exercise-affect relationship by examining individual differences.  Gray's theory of personality was examined in relationship to extraversion and neuroticism as potential moderators of the acute exercise-affect relationship.  Individual differences in personal goal construal were viewed within Ford's control theory model of conscious self-regulation.  Karoly's Goal Systems Assessment Battery (GSAB) that measures the directive, regulatory, and arousal functions of goals measured these differences in personal goal construal.  A sample of 48 participants completed the following three 30-min conditions: control, 55% and 70% of VO_2max exercise.   State anxiety, positive and negative affect were collected immediately, 10 and 20 min post-exercise.  Results for state anxiety indicated that temperaments and individual differences in goal construal significantly (p < .05) accounted for post-exercise anxiety, 19.8% to 24.7%; positive affect, 24.3% to 26.5%; and negative affect, 19.9% to 44.6% in both exercise conditions.  Neuroticism and extraversion are discussed in terms of Gray's (1987) theorized neuronal systems: the behavioral activation system (BAS) and the behavioral inhabition system (BIS).  Results suggested the importance of the BIS when examining affective responding in an acute bout of exercise.  Individual differences in goal construal are discussed within Ford's control theory model of conscious self-regulation.  The present investigation extended past research by demonstrating the importance of personal goal construal on affective responding in response to exercise and the importance of neuroticism in accounting for a significant amount of negative affect responding in an acute bout of exercise.