GSR and neoplasm: In our study, the indicator of glutathione reductase level tends to be increased in both tumor and peritumoral tissues at Grade I. It is significantly elevated in the peritumoral zone, but in Grade II tumor tissue and in the peritumoral zone at Grade IV it does not differ from the adjacent noncancerous tissues, although it is significantly reduced in both zones at Grade III and in the tumor tissue at Grade IV.