The cyclic voltammetry (CV) was used for the measurement of the plasma total antioxidant capacity from two types of patients. The first one consisted of 29 volunteers (men aged 18-21 years) who were administered placebo or silymarin at a dose of 858 mg/day. After two months of silymarine administration, CV revealed a statistically significant increase in total antioxidant capacity compared to placebo. No statistically significant changes in TBARS, SH-groups, creatininin, urea, and uric acid concentrations were found. The second group under study comprised 49 patients with chronic renal disease during dialysis therapy. After dialysis, CV revealed a decrease of total antioxidant capacity in the plasma, which was equivalent to a decrease in creatinine, urea and uric acid. CV was performed using a system consisting of a working glassy carbon electrode, an auxiliary platinum electrode, and a reference saturated calomel electrode; a linear change of voltage of 200 mV/s was applied. CV is a simple and relatively reliable method for assessment of body antioxidant status. It is also time and cost effective.