A rate of protein oxidative destruction may be estimated from the reaction of the resultant carbonyl derivatives of amino acids reaction with 2,4-dinitrophenyl hydrazine. The procedure for estimation of 2,4-dinitrophenyl hydrazones was modified for clinical application. The initiating effect of nonenzymatic components (Fe(3+)-ascorbic acid, Fe(2+)-O2, Fe(2+)-H2O2) was in the metal-catalyzing oxidation of proteins. Estimation of derivatives of 2,4-dinitrophenyl hydrazones in tissues may serve as a pattern of protein oxidative modification during oxidative stress in the body.