| Abstract | The role of free radicals (FR) in the pathogenesis and in the progression of many diseases has been often discussed, but not widely investigated. However, the total antioxidant capacity in the serum seems to be of great evidence. Total antioxidant capacity was determined using oxygen absorbance capacity assay (ORAC) in serum of patients suffering from depression, schizophrenia, Alzheimer's disease (AD), anorexia nervosa, Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Aids-encephalopathy, diabetic polyneuropathy (PNP), cardiomyopathy (CM), renal disease, and healthy individuals as controls (C). The results showed that the total antioxidant capacity in serum decreased significantly (p < 0.01) by 24, 20, 13, and 17% for anorexia nervosa, Aids-encephalopathy, PNP and CM respectively. In serum of patients with renal disease significantly elevated antioxidant capacity was found. The data indicated that increased oxidative stress can be involved in the pathogenesis or in the progression of PNP and CM. Decrease of serum antioxidant capacity in patients with anorexia nervosa and Aids-encephalopathy are probably due primarily to malnutrition and secondly to insufficient antioxidant and immune system. In renal disease, the accumulation of urea in serum seems to be responsible for high antioxidant capacity. In contrast, there were no changes in PD, AD, depression syndrome and schizophrenia. |