Fifty-one neurologically normal children (34 boys and 17 girls) aged 1 month to 11.5 years (median, 6.5 years) who had been referred to our unit were prospectively studied during a 3-year period. They suffered from chronic or recurrent respiratory problems (chronic cough, n = 18; recurrent pneumonia, n = 14; apnea episodes, n = 8; asthma/wheezing, n = 7; posterior laryngitis, n = 4) that were hitherto unexplained and/or had not responded satisfactorily to medical treatment such as antibiotics, inhaled or oral steroids, and β2-agonists. Sixteen of 51 patients had mild and occasional GI symptoms (regurgitation, n = 14; abdominal pain, n = 2) that had never caused medical consultation or self-medication, whereas none had dysphagia or other symptoms suggesting swallowing problems (ie, gagging or choking with feeds, excessive salivation, globus sensation in the throat) or failure to thrive. Patients with recurrent pneumonia had no laboratory evidence of humoral or cellular immune deficiency. All patients had been tested for total IgE (paper radioimmunosorbent test) and specific IgE (radioimmunosorbent test) for aeroallergens and major food allergens (cow’s milk, egg, wheat, maize, rice, soy, fish, shellfish, and peanut), All but two patients had normal IgE levels (paper radioallergosorbent test); and one of these two patients, who had cow’s milk-sensitive eczema in the first few months of life, had mildly raised levels of IgE to wheat, rice, and maize but had not responded to an exclusion diet. Sweat test results were normal in all 27 patients tested. Cardiac, neurologic, and metabolic abnormalities were excluded by appropriate investigation in all infants with apnea episodes. No patient had a history or clinical examination suggesting congenital or acquired anatomic abnormalities of the cardiopulmonary system such as bronchopulmonary dysplasia, bronchiectasia, or congenital heart disease; and in all patients, respiratory symptoms had begun after the first 2 weeks of life. Assuming that pulmonary aspiration of material refluxing from the stomach does not occur in normal individuals, we considered it unethical to subject healthy infants and children to a radionuclide investigation in order to obtain a normal control group. The parents of recruited patients gave written informed consent to all investigations, according to the protocols previously established by the Department of Pediatrics and approved by the hospital Ethics Committee.