Inhibition of return (IOR) is modulated by task set and appears later in discrimination tasks than in detection tasks. Several hypotheses have been suggested to account for this difference. We tested three of these hypotheses in two experiments by examining the influence of cue and target level of processing on the onset of IOR. In the first experiment, participants were required to respond to both the cue and target. The pattern of results showed that deeper processing of the cue or target advanced the onset of IOR. In the second experiment, participants were not required to respond to the cue and a reverse pattern of results emerged, which replicated the general findings in cuing tasks. We conclude that in more-demanding tasks, an additional process slows down the processing of a nonpredictive cue in order to enhance the processing of the target. (Contains 4 figures, 1 footnote and 2 tables.)