This ms. reports the first instance of a reversal of the mere exposure effect: spider fearfuls preferred new spider pictures over previously presented ones. The reversed MEE occurred after threatening materials (spider pictures) were presented to spider fearfuls in an unpleasant detection situation. The paper contributes to the understanding of the mere exposure effect and of the biased cognitive processes in specific fears and phobias. The reversed MEE relates to the clinically relevant processes of habituation and sensitization.