Protein carbonylation is an irreversible oxidation process leading to a loss of function of carbonylatedproteins. Carbonylation is largely considered as a hallmark of oxidative stress, the level of protein carbonyl-ation being an indicator of the oxidative cellular status. The method described herein represents anadaptation to the commonly used 2,4-dinitrophenylhydrazine (DNPH)-based spectrophotometric methodto monitor protein carbonylation level. The classical final sample precipitation was replaced by a gelfiltration step avoiding the tedious and repetitive washings of the protein pellet to remove free DNPHwhile allowing optimal protein recovery.This improved protocol here implemented to assay protein carbonylation in plant leaves can potentiallybe used with any cellular extract.