It has been suggested that metallothionein (MT) not only can regulate essential metals and detoxify toxic metals, but that MT can also play a significant role as an antioxidant and can be induced by oxidative stresses other than metals. This study is aimed at investigating the effect of hydrogen peroxide (H2O2), and the combined effect of H2O2 and cadmium (Cd) on MT induction and condition index (CI) in dogwhelks Nucella lapillus. Adult male dogwhelks (27 +/- 1 mm in shell length) were exposed for 20 days to (1) control (filtered natural seawater only); (2), 0.50 ppm Cd; (3) 2.0 ppm H2O2 + 0.50 ppm Cd; (4) 1.0 ppm H2O2 + 0.25 ppm Cd; (5) 2.0 ppm H2O2; (6) 1000 ppm H2O2 or (7) 1000 ppm H2O2 + 0.50 ppm Cd. The concentration of MT in the Leiblein gland of N. lapillus was quantified using the silver saturation method. MT or MT-like proteins in the animals were induced by Cd (0.5 ppm), H2O2 (2.0 ppm) or Cd + H2O2, indicating that MT in this gastropod species can be induced by either metal or oxidative stresses. Exposure to high H2O2 (1000 ppm) alone or combined with Cd, and exposure to Cd (0.50 ppm) or H2O2 (2.0 ppm), resulted in significant weight loss, indicated by a reduction of CI. However, CIs of groups (3) and (4) were similar to that of the control suggesting that Cd antagonistically reduces toxicity caused by H2O2 since Cd-induced MT may have a protective function against hydroxyl radicals.