Forming an implementation intention (‘If I encounter situation X, then I'll perform behaviour Y!’) is thought to increase the likelihood that the person will detect a good opportunity to act. Experiment 1 found support for this hypothesis in a novel context where detection of the specified cue was very difficult. Experiments 2 and 3 extended existing paradigms to test whether this improved cue detection has costs in terms of increased false positives and/or slower responses to ambiguous stimuli. This hypothesis was not supported. Forming an implementation intention led to more accurate (Experiment 2) and faster (Experiment 3) responses to the specified cue without compromising responses to non-relevant, or ambiguous, stimuli. Overall, the findings suggest that forming an implementation intention is an effective self-regulatory tool because the specified cues are discriminated swiftly and with precision. Copyright © 2004 John Wiley & Sons, Ltd.