Marine gastropods, exposed to anthropogenic pollution, accumulate high chemical concentrations in their tissues, especially in the digestive glands. An evaluation of the impacts of cadmium (Cd) and permethrin (Perm), coupled with reproductive events (pre-spawning and post-spawning phase) throughout the year, was attempted by measuring catalase (CAT), a biomarker of defence, on Hexaplex trunculus experimentally exposed for 48 or 96 h. Specimens of gastropods were sampled from Bizerta Lagoon (Tunisia). The results show that CAT activity increased in gastropods exposed to the three cadmium concentrations (C1 Cd, 100 μg L(-1); C2 Cd, 200 μg L(-1); and C3 Cd, 300 μg L(-1)) and to the three permethrin doses (C1 Perm, 100 μg L(-1); C2 Perm, 150 μg L(-1); and C3 Perm, 200 μg L(-1)) tested. A decrease in CAT was noted in the digestive gland of the H. trunculus exposed to permethrin at the concentration of 200 μg L(-1) during the pre-spawning and post-spawning phases. H. trunculus in post-spawning was more sensitive to cadmium and permethrin than in the pre-spawning phase. The biochemical responses to pollutants (cadmium and permethrin) represented by CAT may act as a biomarker of exposure in this species.