The study was conducted on 31 patients suffering from transitional bladder carcinoma (TBC). They were divided as follows : 1.Primary group : patients who are to be subjected for tumour resection for the first time. 2…Recurrent group : patients who subjected to tumour resection for more than one time. Further grouping was performed following histopathological examination of tumour issue into grade 2 and grade 3. In these groups, the oxidative stress (OS) and the detoxification mechanism mediated by glutalhione (GSM) and its related enzymes were evaluated indirectly, by measuring the changes in the following parameters: plasma MDA-LM, plasma peroxynitrite, plasma and tissue thiol as a marker of GSH, plasma and tissue glutathione reductase (GR), and tissue glutathione -S- transferase (GST). The above parameters were also studied in a control group of 1 1 healthy subjects. The plasma MDA-LM concentration in both groups was increased significantly in grade 2 and grade 3 as compared with control group (p<0,005). In addition plasma thiol level in both groups was significantly lower in grade 2 and grade 3 than control group (p = 0.01). While plasma GR activity was significantly increased in both groups as compared with control group (P<0.()5). 'I'herefor an increased OS in patients with TBC can be most likely concluded. A significant increase in plasma peroxynitrite was shown only in grade 2 - recurrent group as compared with control group (P = 0.002). This finding may point to the activation of immune system to produce nitric oxide after BCG (Bacillus, Cahnette, Guerin) admission In the tissue, a significant increase in thiol concentration was shown in the both groups as compared with control group (P = 0.02), while a significant decrease in the activity of GR and GST were observed in both groups as compared with control group (PO.05). Suggesting an increase in the delivery of many toxic agents including reactive oxygen species (ROS) and drugs capable of redox cycling into cancer cells.