Decreased antioxidant status in depression, characterized by a significantly reduced level of non-enzymatic antioxidant molecules, such as tryptophan, tyrosine, vitamin E, ascorbic acid, alfa-tocopherol, zinc, and GSH (Kodydková et al. 2009; Maes et al. 2011a), is usually connected with a fall in GPx, CAT, and SOD activity in blood although in some other studies an increase or no differences in GPx and SOD activity were described (Bilici et al. 2001; Galecki et al. 2009; Rybka et al. 2013; Smaga et al. 2015). This evidence concerns the gene CAT and major depressive disorder.