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Mice placed into novel cages showed elevations of plasma levels of corticosterone. This response was of greater magnitude when the more novel of two cages was used. When mice had a piece of aluminum foil or cardboard available in the novel cages, they avidly chewed these substances. In the high novelty cage, the presence of either foil or cardboard reduced the magnitude of the plasma corticosterone response at 30 and 60 min. Mice exposed to novel cages for 30 min on each of 6 consecutive days showed a decline in chewing across days, although chewing still occurred during the last exposure. The plasma corticosterone response increased from the first to the sixth day of exposure, although the availability of foil in the high novelty cage reduced this response across days. The availability of a highly palatable food (peanut butter chips) evoked little chewing in the high novelty cage and had no effect on the plasma corticosterone response at 60 min. The results suggest that the chewing of nonedible substances can reduce the response of the pituitary-adrenal system to novelty and may therefore serve as an arousal-regulating mechanism in this species.