Metallothioneins (MTs) protect the cell against reactive forms of oxygen, ionizing radiation, pharmacological agents and mutagens. Metallothioneins are also responsible for neoplastic cell resistance to cytostatic drugs. The aim of this study was to determine the MT level in cell fractions as well as to determine whether there is any change in the concentration of these proteins in a neoplastic cell, and in which cell fractions this change takes place. The neoplastic tissue examined was histopathologically ductal carcinoma invasive, and the control tissue was mastopathic tissue with proliferated connective and glandular tissue. The level of MTs was determined using cadmium isotope (109Cd). It was determined that there was an increase in MT level in the neoplastic tissue, the highest level being found in the mitochondrial fraction obtained from the control and mastopathic tissues. The greatest changes in MT concentrations in breast carcinoma were observed in the nuclear and cytosol fractions. In the nuclear fraction in the breast carcinoma tissue, the MT level was almost three times that of the control group.