It is concluded that uric acid stores increase during estivation and that they may be consumed during arousal as a significant antioxidant defense against the damaging effects of reoxygenation. The sustained increase in the uric acid oxidative product (allantoin) which occurs during arousal, appears more easily related to non-enzymatic oxidation than to the action of urate oxidase. In fact, the activity of this enzyme shut down during estivation in all the studied tissues while a partial though sustained recovery was only observed in the midgut gland. The hypothesis of a physiological role of uric acid as a non enzymatic antioxidant should be complemented with studies of other enzymatic (superoxide dismutase, catalase, glutathione perox- idase) and non-enzymatic (glutathione) antioxidant defences in P. canaliculata. Also, the possible role of urate oxidase in nitrogen recycling in active snails should be further studied in this species.