In resurgence, an operant behavior that has undergone extinction can return ("resurge") when a second operant that has replaced it itself undergoes extinction. The phenomenon may provide insight into relapse that may occur after incentive or contingency management therapies in humans. Three experiments with rats examined the impact of several variables on the strength of the resurgence effect. In each, pressing one lever (L1) was first reinforced and then extinguished while pressing a second, alternative, lever (L2) was now reinforced. When L2 responding was then itself extinguished, L1 responses resurged. Experiment 1 found that resurgence was especially strong after an extensive amount of L1 training (12 as opposed to 4 training sessions) and after L1 was reinforced on a Random Ratio schedule as opposed to a variable interval schedule that was matched on reinforcement rate. Experiment 2 found that after 12 initial sessions of L1 training, 4, 12, or 36 sessions of Phase 2 each allowed substantial (and apparently equivalent) resurgence. Experiment 3 found no effect of changing the identity of the reinforcer (from grain pellet to sucrose pellet or sucrose to grain) on the amount of resurgence. The results suggest that resurgence can be robust; in the natural world, an operant behavior with an extensive reinforcement history may still resurge after extensive incentive-based therapy. The results are discussed in terms of current explanations of the resurgence effect. (Contains 3 figures.)