Children under age 2 years presenting for unscheduled care to the ED with a diagnosis of moderately severe bronchiolitis (as defined by inclusion/exclusion criteria below) will be approached for entry into the study. Recruitment will only occur when Research Assistants are on duty, is projected to include regular working hours Monday-Friday as a minimum and will continue until the calculated sample size has been obtained (anticipated 12 months). Initial routine assessment by the ED staff will identify potential subjects and Research Assistants will be notified to apply the inclusion/exclusion criteria and obtain informed consent if appropriate. Recruited subjects will be randomized to receive treatment in a double blind fashion with inhalation of nebulized study solution containing either 7% hypertonic saline (HS, study group) or 0.9% saline (NS, control group). Each dose of study solution will also contain a standard dose of bronchodilator (salbutamol, 0.15 mg/kg; 0.03 ml/kg of 0.5% salbutamol nebulizer solution) added by the ED staff. Each participant will remain on the same allocation throughout the protocol and receive 3 consecutive 4ml doses of the assigned study solution with salbutamol over a 1-hour period.