There is now reliable evidence that heightened positive affectivity is associated with a distinctive pattern of attentional selectivity, favouring emotionally positive information. While this has invited speculation that differential attentional responding to positive information may directly contribute to the determination of this emotional temperament, the causal basis of their association as yet remains unknown. We addressed this issue by experimentally manipulating selective attentional response to positive information, using a cognitive bias modification variant of the attentional probe task, and examining the impact of this attentional manipulation on positive emotional reactivity to a subsequent success experience. The findings support the hypothesis that individual differences in selective attentional response to positive information can make a causal contribution to variation in positive affectivity. Copyright © 2012 John Wiley & Sons, Ltd.