Extinction-induced resurgence is the recurrence of previously reinforced behavior when another behavior is placed on extinction (Lieving, Hagopian, Long, & O'Connor, 2004). This phenomenon may account for some instances of treatment relapse when problem behavior recovers during extinction-based treatments. The current study sought to determine whether resurgence of problem behavior would reliably occur with 5 participants who received treatment with FCT. Results showed that problem behavior reemerged for all but 1 participant when the communicative response was exposed to extinction or thin schedules of reinforcement. These findings suggest that resurgence may account for some instances of response recovery during treatment, and that the described procedure may be useful for the further study of resurgence and eventual prevention of this phenomenon. (Contains 4 figures.)