Antioxidant enzymes: catalase (CAT) [EC 1.11.1.6], peroxidase [EC 1.11.1.7], glutathione reductase (GSSGR) [EC 1.6.4.2] and glucose-6-phosphate dehydrogenase (G6PDH) [EC 1.1.1.49] were investigated in terrestrial Helix aspersa (O.F. Müll.) and aquatic Pomacea bridgesi (Reeve). The activity was determined in the heamolymph and homogenates of hepatopancreas and foot muscle. No CAT and peroxidase activity was detected in the hepatopancreas and foot muscle of P. bridgesi, and its haemolymph displayed a very low CAT activity (0.005 U/mg of protein). In H. aspersa the highest activities (U/g) observed for CAT and GSSGR in the hepatopancreas were 0.40, and 1.05, respectively; for peroxidase and G6PDH in the foot muscle the respective values were 1.22 and 0.22. The activities of antioxidant enzymes determined in both snail species are much lower than the corresponding values for mammalian tissues.