We assessed whether radon inhalation provided protection from carbon tetrachloride (CCl4)-induced hepatic and renal damage in mice. Mice were subjected to intraperitoneal injection of CCl4 after inhaling approximately 18 kBq/m(3) radon for 6 h. Radon inhalation significantly increased total glutathione (t-GSH) content and glutathione peroxidase (GPx) activity in the liver and kidney. Injection of CCl4 was associated with significantly higher levels of glutamic oxaloacetic transaminase (GOT) and alkaline phosphatase (ALP) activity and creatinine level in serum, and pretreatment with radon significantly decreased the GOT and ALP activity and creatinine level associated with CCl4 injection, suggesting that radon inhalation alleviates CCl4-induced hepatic and renal damage. The t-GSH contents and GPx activity in the liver and kidney of animals pretreated with radon were significantly higher than those of the CCl4-only group. These findings suggested that radon inhalation activated antioxidative functions and inhibited CCl4-induced hepatic and renal damage in mice.