Nasal airflow resistance was measured in order to study physiological changes in the upper airway before and after adenoidectomy. The posterior method was better for measuring the state of the posterior portion of the nasal cavity, as compared with the anterior method. The posterior method was modified by improving the pressure piece, the size of which had been inadequate for insertion into a child's mouth. A positive correlation was found between the adenoidal-nasopharyngeal ratio examined on X-ray film and the nasal airflow resistance both before and after surgery. Also there was a positive correlation between the weight of the resected adenoids and nasal airflow resistance preoperatively. Nasal airflow resistance was found to be significantly higher in patients who snored, breathed by mouth or had nocturnal breathing disorders than in those without these symptoms.