110 patients under three years of age with pneumonia were admitted to this hospital in a period from August of 1982 to March of 1983. There were 68 males and 42 females. The patients were randomly divided into Group A and Group B .The symptoms and signs, the laboratory data, and the severity and duration of the illness of the patients of both groups were similar.After admission, laboratory examinations including WBC counts, throat swab cultures and determinations of immunity function were performed and chest x-ray films were taken for all the patients. Regular treatments were given to all of them but the patients of Group A received TDP radiation in addition.After comparing the clinical courses of the two groups, the authors found that TDP could cause more rapid disappearance of cough and moist rales in the lungs, shorten the time of recovery and the whole course of hospitalization, and hasten the absorption of pulmonary infiltrations as seen from the x-ray films. Furthermore, TDP is helpful to promote the immunity function by raising many immune indices. And the rate of lymphocyte transformation was also increased. Its influence on the bringing down of the fever to normal is not very remarkable.It is concluded that TDP radiation is a simple, safe and effective treatment for pneumonia and it is suitable to be used in children.