It has previously been shown that when picture pairs are repeated across blocks in a post-cue naming task, former distractors are named faster than former targets: the "negative repetition effect" (Mayall, Humphreys, & Kotsanis, 2002). In the present study the time course of this effect was examined. Experiment 1 demonstrated that the effect became apparent after a lag of only two intervening trials, with former targets being named faster than former distractors after a lag of zero trials. Experiment 2 used a new baseline condition with repeated picture pairs for which no response was required on the first presentation. Comparisons with this baseline indicated that the negative repetition effect is the result of suppression of former targets as opposed to facilitation of former distractors. The results support the proposal of Mayall et al. that the negative repetition effect reflects a form of speech monitoring that is applied when there is competition in the process of mapping from semantics to name representations.