Background: Cytokines such as IL-2 are thought to be important in the pathogenesis of respiratory tract inflammation. Cytokine levels in nasopharyngeal aspirates (NPAs) have been used as a measure of respiratory inflammation in children with viral infections, but it is unclear whether they reflect levels in the lower respiratory tract. Objective: We sought to assess the correlation between IL-2 levels in the nasopharyngeal and endotracheal secretions of children intubated with respiratory syncytial virus (RSV)–positive bronchiolitis. Methods: NPA and endotracheal aspirates were collected concurrently from intubated infants with RSV-positive bronchiolitis. IL-2 levels were assayed by ELISA, and the results were compared according to collection site. Results: Nine paired specimens were collected. IL-2 levels ranged from 31 pg/mL to 8040 pg/mL. No significant difference was found in the geometric mean IL-2 values from the 2 collection sites. The intraclass correlation coefficient between NPA IL-2 levels and endotracheal aspirate IL-2 levels was 0.83. Conclusion: IL-2 levels in NPAs are comparable with those in the lower respiratory tracts of infants with RSV-positive bronchiolitis. NPA cytokine levels provide a simple and useful means of assessing respiratory tract inflammation. (J Allergy Clin Immunol 1998;102:618-20.)