The present study deals with the effect of imagery ability on treatment outcome in spider phobias. Thirty-eight spider phobics completed the Questionnaire on Mental Imagery (QMI) and the Spider Questionnaire (SPQ). Subjects also went through a behavioral approach task (BAT) during which heart rate and avoidance behavior were measured. Each subject was then given one-session treatment as described by Ost. Immediately after treatment, SPQ and BAT data were again obtained. On the basis of their QMI scores, subjects were assigned to a 'good', 'moderate', or 'poor' imagers group. Neither pre-treatment nor post-treatment measures were found to vary as a function of imagery ability. Thus it appears that, at least for specific phobias such as spider fear, imagery ability is not a relevant variable for predicting the effects of in vivo exposure.