Glutathione content and glutathione S-transferase activity have been studied in human bladder specimens obtained from controls and from patients with superficial transitional cell carcinoma (tumor samples and peri-tumor normal tissues from the same patient). After combining an earlier study from our laboratory with the additional material presented (9 healthy controls and 25 transitional cell carcinoma patients), it can be observed that glutathione S-transferase activity was significantly greater in tumor than in peri-tumor normal tissue (34 patients, p < 1 x 10(-7)) or in normal mucosa (17 controls, p < 1 x 10(-3)). Glutathione content was significantly greater in tumor than in peri-tumor normal tissue (p < 5 x 10(-3)) or in normal mucosa (p < 2 x 10(-2)), with this increase being evident only in smokers. When comparing normal mucosa and peri-tumor samples no significant differences were found either for glutathione S-transferase activity or for glutathione content. Results demonstrate the relationship between the glutathione S-transferase/glutathione system and development of transitional cell carcinoma, as well as its role in cellular resistance to chemotherapy.