Catalase (CAT), glutathione reductase (GR), glutathione S-transferase (GST), and thiobarbituric acid reactive substances (TBARS) were measured together with cadmium (Cd) toxicity and accumulation in newly molted adults of Oncopeltus fasciatus (Dallas) exposed to the metal in drinking water. Insects were provided with either 200 or 20 mg Cd/liter (96-h LC₃₀ and LC₁₀, respectively) or with tap water for 1, 3, 5, and 7 d. Insects exposed to either concentration accumulated Cd in a time-dependent manner. Peroxilipids measured as TBARS were significantly elevated (1.7- to 1.9-fold) from day 3 in insects exposed to 200 mg Cd/liter, whereas TBARS levels of insects exposed to 20 mg Cd/liter were unaffected. Significant 2.3- and 1.9-fold inductions were observed in GR activity of insects treated with 200 mg Cd/liter for 5 and 7 d, respectively, while CAT and GST levels were not affected by Cd exposure. These findings indicate that 200 mg Cd/liter causes oxidative stress to O. fasciatus and induces GR activity, suggesting that glutathione may be involved in protection against Cd oxidative damage in this species.