This study was carried out on patients suffering from recurrent lower respiratory tract infections in the form of recurrent pneumonia and recurrent/chronic bronchitis. These patients were admitted into the inpatient departments of the Specialized Children’s Hospital, Cairo University, over a period of eight months from April to December 2002.Diagnosis of patients was based on careful history taking, clinical examination and specific investigations.The total number of patients was 40, 25 males and 15 females, their ages ranged between 1 to 10 years with a mean age of 4.3 years ± 2.6 They all had recurrent attacks of severe lower respiratory tract symptoms more then 3 times a year, with a mean duration of present illness of 2 weeks.The main presenting symptom was dry cough (62.5% of cases), followed by dyspnea (50% of cases).The main findings by general examination were cyanosis (12 patients (30%)) followed by stunted growth ( 7 patients (17.5%))Chest examination revealed intercostal retractions in 50% of patients, impaired note in 65% of patients, fine crepitations in 65% of patients, coarse crepitations in 35%, and wheezes in 22.5% of patients.As regards the final diagnosis, 35% had lobar pneumonia, 2 of them were complicated by pleural effusion, 30% had bronchopneumonia, and 35% had chronic bronchitis.The aim of our study was to assess the level of the immunoglobulin G subclasses in these patients with recurrent respiratory tract infections. Our results revealed deficiency of IgG1 in only 1 patient and deficiency of IgG2 in 9 patients (22.5%).There was a strong relation between serum levels of IgG and IgG1. On the other hand, no positive relation was obtained between the serum levels of IgG and IgG2.Regarding the relation between IgG1 and IgG2, deficiency in IgG2 was accompanied by a compensatory elevation of IgG1.Again there was a clear relation between IgG subclass deficiency and the severity of lower respiratory tract infection.