Five rats served in an experiment with multiple extir ction fixed-interval schedules of reinforcement. While the fixed-interval schedule was kept constant at 60 s, the fixed extinction period was varied frorn 10 to 160 s. Pauses during the fixed-interval schedule decreased systematically with increases in the previous extinction period. Pausing was under control of both time to the next primary reinforcement signaled by the discriminative stimulus associated with the fixed-interval schedule and time since the last primary reinforcement, signaled by the duration of the extinction period.