The objective of this work was to determine the effect of Au NPs of different sizes (20 and 100 nm) and different concentrations on parameters of the redox status, such as the total antioxidant status, lipid and protein oxidation markers, and antioxidant enzyme activities (glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase) in selected healthy and cancer cell lines derived from different tissues. The gene discussed is CAT; the disease is cancer.