In most circumstances, a nasal route for the delivery of pulmonary aerosol medications is rarely considered; however, in specific instances, this route may be quite useful. Consider, for example, the delivery of aerosol treatments during humidified high-flow nasal cannula use in pediatric critical care, or continuous aerosol delivery via cannula for medications with short durations of action. The goal of this study was to evaluate the potential for delivering aerosols via nasal cannula through in vitro studies of aerosol output and size. The system utilized for testing included an Aerogen Solo nebulizer downstream of a heater/humidifier system, followed by a nasal cannula and an aerosol collection apparatus. Adult, pediatric, and infant cannulas were tested with and without an inhalation-only breathing simulator. The cannulas were driven by 3 lpm (50 psig) oxygen flows. Dose quantification was performed using radioisotope techniques. Total cannula output and system losses were measured. Aerosol size measurements were made from the nebulizer, from the heating tube, and from the prongs of the adult and pediatric cannulas, using laser-diffraction techniques. Total cannula output ranged from 8.4-25.1% and 18.6-26.9% of loaded dose, without and with the addition of inhalation flows. Volume median diameters were 2.2 +/- 0.2 microm from the adult cannula and 1.9 +/- 0.3 microm from the pediatric cannula. Ninety percent of the aerosol volume was in sizes smaller than 4.2 +/- 0.4 microm (adult) and 3.8 +/- 0.5 microm (pediatric). System losses were highest in the nebulizer-humidifier connectors, heated tube, and humidifier. Losses in the nebulizer were very low (2.2-3.5%). This study demonstrates that aerosols can be efficiently delivered through a humidified high-flow nasal cannula system. Further study is required to determine if this route is viable for pulmonary delivery.