Individual differences in resting asymmetrical frontal brain activity have been found to predict subsequent emotional responses. The question of whether frontal brain asymmetry can cause emotional responses has yet to be addressed. Biofeedback training designed to alter the asymmetry of frontal brain activity was therefore examined. Eighteen right-handed female participants were randomly assigned to receive biofeedback training designed to increase right frontal alpha relative to left frontal alpha (n = 9) or to receive training in the opposite direction (n = 9). Five consecutive days of biofeedback training provided signals of reward or nonreward depending on whether the difference between right (F4) and left (F3) frontal alpha exceeded a criterion value in the specified direction. Systematic alterations of frontal EEG asymmetry were observed as a function of biofeedback training. Moreover, subsequent self-reported affect and facial muscle activity in response to emotionally evocative film clips were influenced by the direction of biofeedback training.