Tissue levels of adenosine deaminase, malondialdehyde, total glutathione and Selenium were measured in samples from 51 femal patients presented with breast masses. --Twenty five apparently normal breast tissue samples were also included as controles. There were 21 patients with rnvasive breast cancer, 17 patient with fibrocystic. disease and 7 patients with fibroadenoma. Fresh tissue samples were obtainad at time of operation and instantly frozen using liquid Nitrogen, then homogenized and centrifuged to get a supernatant which the biochemical assays were done. Adenosine deaminase was estimated by using giusti method, the mean levle of it in invasive breast cancer tissue was 47.956 mu/mg protein significantly higher than that of the control 40.115 mU/mg protein. Malondialdehyde a product of lipid peroxidation was measured to reflect free radical activities in breast tissues by using okahawa method, it was found to be significantly lower in Invasive breast cancer tissue 0.1748 nmol/mg protein, than that of controls and other benign tumors or lesions of the breast. Total glutathione obtained using a modified Ellman method. Invasive breast cancer the tissue level mean was 8.467 nmol/mg protein , which is lower than that of the controls x = 9.450 unol/mg protein). Selenium a trace element and a part of glutathione peroxidase enzyme i.e part of scavenging mechanisms of free radicals, it was measured by using a nonflammable atomic absorption, it was found• be significantly lower in invasive breast cancer tissue (x = 2.572 ug/gm tissue) when compared to controls (x= 3.812 ug/gm wet tissue). Correlations were drawn etween adenosine deaminase, glutathione and Selenium, each with malondialdehyde and between glutathione and Selenium in each group of patients and also in controls. From the mean value of each group and from correlations, we concluded from this study that;'adenosine deaminase and Selenium could be used as parameters for the diagnosis of malignant tumors of the breast, while changes in tissus level of malondialdehyde and glutathione levels could be only a reflection of the status of the radicals and their scavengers in the breast tissue.