Little is known regarding effects of components of the exercise stimulus (e.g., intensity, duration) on affective responses. The effect of varying levels of exercise intensity was examined for state anxiety (SA), positive affect (energetic arousal; EA), and negative affect (tense arousal; TA). Twenty subjects (M age = 22.6 years; M VO2 max = 47.8 ml.kg-1.min-1) participated in 3 randomly assigned conditions: (a) no exercise (control), (b) cycling@ 55% VO2max, and (c) cycling@ 70% VO2max. After being seated on an exercise bike, subjects completed the affect measures and were then told what condition they had been assigned for that day. Subjects either exercised or sat quietly on the bike for 30 min. Affect measures were obtained during exercise (or control), upon cessation of each condition, and then during the 30 min post-condition period. No changes occurred for the control condition on any variables. SA increased (p < 0.05) for both intensities during exercise followed by a significant post-exercise reduction only in the 70% VO2max condition. EA increased (p < 0.05) during exercise and remained elevated following both exercise intensities; increased EA was maintained to a greater extent following the 70% intensity condition (p < 0.05). These findings suggest that aerobic exercise (55-70% VO2max) elicits not only decreases in negative feeling states (state anxiety) but also increases in positive affect. Further, there is some evidence that such changes may be dependent on exercise intensity.