This study deals with the removal of nitrogen oxides from flue gases using the acidic urea process. The chemical hydrolysis of nitrous acid, which leads to NO formation, is avoided by nitrous acid reaction with urea. Products of this reaction are gases, e.g. CO2 and N2, which can then be directly released into the atmosphere. The aim here is to determine the kinetic parameters of the chemical reaction of nitrous acid with urea. Experiments are performed in a closed stirred reactor. The manometric method (measurement of the pressure versus time curve) leads to the determination of the concentration of HNO2 and then to the chemical rate versus time. Operating parameters are the concentration of urea (333-3330 mol m-3), the pH (0.75-1.25), and the temperature (3-40-degrees-C). The experimental results are as follows: the order relative to nitrous acid is 1; the rate constant decreases with pH; the influence of temperature on the rate constant can be expressed by (pH = 1) k = 1.82 x 10(8) exp(-(60400/RT)) (SI units).