We examined the activity of striatal superoxide dismutase (SOD) in two acute pharmacological models of Huntington's disease (HD), and compared it with SOD activity in the striata of mice transgenic for the HD mutation. Total SOD, and Cu/ZnSOD activities increased in young transgenic mice, but decreased in older (35 week) mice. We consider that the increased enzyme activity represents a compensatory mechanism to protect cells from free radical-induced damage, but the system becomes insufficient in older animals. Major decreases in SOD activity were also observed both after quinolinic acid and 3-nitropropionic acid intrastriatal injections. The present results indicate that in both types of HD models striatal oxidative damage occurs, and that it is associated with alterations in the cellular antioxidant system.