This study was designed to investigate the protective effects of two traditionally used Turkish medicinal plants, Camellia sinensis (CS) and Urtica dioica L. (UD), beverages used against chemical carcinogen trichloroacetic acid (TCA)-exposure in rats. The preventive potential of the plant infusions was evaluated by measuring the level of serum marker enzymes, aspartate aminotransferase (AST), alanine aminotransferase (ALT), creatine phosphokinase (CPK), acid phosphatase (ACP), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH); antioxidant defense systems, reduced glutathione (GSH), glutathione reductase (GR), superoxide dismutase (SOD), glutathione-S-transferase (GST) and catalase (CAT); and lipid peroxidation (malondialdehyde, MDA) content in various organs of rats. Twenty four healthy rats were randomly allotted into four experimental groups: A (untreated control), B (only TCA-treated), C (TCA + CS treated) and D (TCA + UD treated). At the end of the 50 days, the plant infusions possessed chemoprotective effects, deduced by the remaining TCA-induced increased serum damage marker enzyme, lipid peroxidation and antioxidative system in rats compared with those of the control and TCA-exposed rats. According to the results, while the levels of AST, ALT and CPK increased in group B, no significant changes were observed in groups C and D. The MDA content slightly increased in tissues of all groups, being higher in group B. Antioxidant enzyme activities such as SOD and CAT increased significantly in the brain, liver and kidney of group B while they did not change significantly except for in the kidney in groups C and D. The GSH level and the ancillary enzyme GR activity did not change significantly in organs of all groups. On the other hand, the drug metabolizing enzyme, GST, activity decreased significantly in the brain, liver and kidney of group D while slight changes were observed for the other groups. The results revealed that TCA exposure induced oxidative stress in rat tissues, however, in plant beverage supplemented groups, a significant protective effect of CS and UD against TCA-induced oxidative injury was recorded. Hence, the study revealed that the constituents present in CS and UD impart protection against carcinogenic chemical induced oxidative injury that may result in the development of cancer. Also the observations, along with changes, suggest that both CS and UD may possess preventive potential during a 50-day protective exposure. Copyright (c) 2007 John Wiley & Sons, Ltd.