The kinetic parameters of the oxidant action of the combination of enzyme horseradish peroxidase (HRP) with hydrogen peroxide in the degradation of methylene blue dye were investigated. Twenty-one percent of color removal was obtained at pH 5.0 and temperature of 30 A degrees C. Under these conditions, the kinetic parameters K (m) and V (max) of enzymatic reactions were determined for hydrogen peroxide in the absence of methylene blue dye (K (m) = 17.3 mM; V (max) = 1.97 mM/min) and in the presence of methylene blue dye (K (m) = 0.27 mM, V (max) = 0.29 mu M/min). By means of analysis of phosphorescence, the presence of reactive oxygen species was detected in the form of singlet oxygen through the redox reaction between HRP and hydrogen peroxide. The existence of this reactive species is directly dependent on the concentration of hydrogen peroxide in the aqueous solution.