This study replicated the effect of Wickless and Kirsch's experiential expectancy manipulation, in which lights and music from hidden sources were used to convince participants that they were responding successfully to suggestions for visual and auditory hallucinations. The hypothesis that the effect is mediated by detection of the manipulation was tested by providing some participants with cues that their experiences were due to actual changes in the physical environment rather than to their responses to suggestion. This hypothesis was not confirmed. A significant effect on suggestibility was obtained only among participants not given cues aimed at enabling detection of the manipulation, and among those provided with the cues, suspicion of the manipulation was negatively correlated with response to suggestion.