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 (H 2 O 2 ), and the combined effect of H 2 O 2 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 H 2 O 2 +0.50 ppm Cd; (4) 1.0 ppm H 2 O 2 +0.25 ppm Cd; (5) 2.0 ppm H 2 O 2 ; (6) 1000 ppm H 2 O 2 or (7) 1000 ppm H 2 O 2 +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), H 2 O 2 (2.0 ppm) or Cd+H 2 O 2 , indicating that MT in this gastropod species can be induced by either metal or oxidative stresses. Exposure to high H 2 O 2 (1000 ppm) alone or combined with Cd, and exposure to Cd (0.50 ppm) or H 2 O 2 (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 H 2 O 2 since Cd-induced MT may have a protective function against hydroxyl radicals.