Free-radical processes were assessed in exhaled air condensates of healthy children and of those suffering from recurrent bronchitis during remission and at the onset of exacerbation. 3 percent hydrogen peroxide-induced chemiluminescence technique was employed with the results recorded by chemiluminometer, manufactured in this country. The data evidence an increase of the total induced chemiluminescence in the patients during exacerbation vs. that in healthy children; such measurements may become a valuable test in the diagnosis of chronic and recurrent pulmonary disease in children.