Estivation enables land snails to survive a prolonged dryness but the return to active state imposes conditions of oxidative stress on internal organs due to a transient large increase in oxygen consumption, which augments mitochondrial production of reactive oxygen species. Therefore, activities of antioxidant enzymes, concentrations of reduced glutathione (GSH) and TBARS as an index of lipid peroxidation, were evaluated in Helix pomatia snails (i) during summer activity, (ii) during estivation, which was induced experimentally, (iii) at the start of arousal from estivation, and (iv) being aroused for 24 h. Estivation induced significant decreases in activity of catalase in the kidney and hepatopancreas and glutathione peroxidase in the kidney. Activity of glutathione reductase was unaffected by estivation/arousal cycle. Summer-active and estivating snails maintained high activity of glutathione transferase. Concentration of GSH was organ-dependent and was positively affected by estivation. Lack of increase in TBARS concentration during estivation/arousal cycle suggests that antioxidant defence system of H. pomatia snails is highly efficacious. In conclusion, permanent maintenance of relatively high activities of the antioxidant enzymes and the high concentration of GSH in H. pomatia snails indicate that they have well-developed strategy of defence against oxidative injury.