The most common products of protein oxidation in biological samples are the protein carbonyl derivatives of Pro, Arg, Lys, and Thr. These derivatives are chemically stable and serve as markers of oxidative stress for most types of ROS. In the traditional ELISA method, protein samples containing low amounts of protein must be concentrated to at least 4 mg/mL by TCA precipitation. However, TCA precipitation results a 20% loss of the total carbonyl values, and loss of protein during precipitation is also expected. In the OxiSelect™ Protein Carbonyl ELISA Kit, protein samples are first allowed to adsorb to wells of a 96-well plate and then react with DNPH. There is no need to concentrate protein in experimental and clinical samples with low amounts of protein (< 4 mg/mL) and the kit requires protein sample as little as 10 μg/mL. Each kit provides sufficient reagents to perform up to 96 assays, including standard curve and unknown protein samples.