767 Electroencephalographic (EEG) frontal asymmetry has been proposed as both a physiologic index and a diathesis or disposition for emotional responding (Davidson, 1992; 1994). This study used a counter-balanced repeated measures design to examine the effect of 30 minutes of cycling exercise at ∼50%V̇O2peak, compared to 30 minutes of rest, on changes in emotional response ∼30 minutes after condition to standardized negative and positive images presented by slide projection (International Affective Picture System, Lang et al., 1988a). Emotional response was measured by EEG and self-ratings of valence and arousal (Self-Assessment Manakin, Lang et al., 1988b) in 13 females and 19 males (23±3 and 25±4y) having moderate levels of cardiorespiratory fitness (V̇O2peak = 41±9 and 53±11 ml·kg−1·min−1, respectively). Consistent with Davidson's diathesis model, response frontal α (lognμV2/Hz) right-minus-left asymmetry was predicted by resting α asymmetry, independent of neutral response (negative: t(29)=1.72, p=.09; positive:t(29)=2.35, p<.03). Valence ratings were weakly related to resting α asymmetry (p<.03). The cycling condition did not alter emotional response as indicated by [1] α asymmetry (negative: F(1,28)=0.04, p=.84, η2=.002; positive: F(1,28)=0.48, p=.49, η2=.017), [2] valence (negative: F(1,28)=0.23, p=.64, η2=.008; positive: F(1,28)=0.88, p=.36, η2=.030), or [3] arousal (negative: F (1,28)=0.15, p=.71, η2=.005; positive: F(1,28)=0.18, p=.67, η2=.007). The β1 and β2 EEG spectra were similarly unaffected by condition. Also, cycling exercise failed to alter positive or negative affect (PANAS, Watson et al., 1988), but it decreased state anxiety (STAI-Y1, 10-item)(F(1,28)=6.56, p=.02, η2=.190). Results did not differ according to gender. In the cycling condition, state anxiety change was not influenced by trait anxiety (STAI-Y2) or pre-condition resting α power asymmetry (F(2,29)=1.21,p=.31, R2adj=.014). These results indicate that moderate intensity cycling exercise lasting 30 minutes does not alter emotional response as measured, despite reducing state anxiety.