Breast cancer is the first of the most common ten cancers in Iraq. Its etiology is multifactorial, oxidativestress and lipid peroxidation being suggested to play important roles in carcinogenesis. The purpose of thisstudy was to investigate the oxidant-antioxidant status in breast cancer patients, by measuring SOD isoenzymeactivities (total SOD, CuZn-SOD, Mn-SOD and EC-SOD) in plasma and breast tumors, and by estimatingthiobarbituric reactive substances (TBRS) in tissue homogenates. General increase in total SOD activity wasobserved in plasma and tissue samples of breast tumors, greater in the malignant when compared to benigngroup (p<0.05). Mn-SOD showed a significant decrease in tissue malignant samples (p<0.05), and insignificantdecrease in plasma malignant samples compared with control and benign samples. Plasma EC-SOD activityin both patient benign and malignant breast tumors demonstrated 3.5% and 22.8% increase, respectively.However, there was a decrease in tissue EC-SOD activity in malignant breast tumors when compared withbenign. A similar tendency was noted for TBRS. We suggest that elevated total SOD might reflect a response tooxidative stress, and then may predict a state of excess reactive oxygen species in the carcinogenesis process. Ifthere is proteolytic removal of the heparin binding domain, EC-SOD will lose its affinity for the extracellularmatrix and diffuse out of the tissue. This will result in a decreased EC-SOD activity, thus leading to an increasein the steady-state concentration of O2- in this domain, and increase in EC-SOD activity in the extracellular fluid.This might explain the results recorded here concerning the decrease in tissue EC-SOD activity and increase inplasma of breast cancer patients.