Peroxynitrite and hypochlorite are oxidants relevant in many pathological situations. We propose a simple spectrophotometric assay to determine antioxidant capacity against hypochlorite and peroxynitrite based on protection against Pyrogallol Red decolorization. The assay can be performed on a microplate and requires minute amounts of material. Standard antioxidants show different reactivities for both oxidants. Antioxidant capacity of blood plasma (anticoagulated with EDTA) of healthy persons was found to be 559 +/-49 mu mol/l and 11.6 +/- 1.2 mmol/l of ascorbic acid equivalents for peroxynitrite and hypochlorite, respectively. (C) 2009 Elsevier Inc. All rights reserved.