Viral upper respiratory tract infection (URI) is one of the most common diseases among toddlers and pre-school children.Complete and effective prevention measures for URI are currently unavailable.

Montelukast (Singulair ) is a selective leukotriene-receptor antagonist that inhibits the cysteinyl leukotriene 1 receptor. It is well tolerated and safe even in young children. Montelukast is an effective treatment for asthma (and allergic rhinitis from 1 year of age. Infections with viruses causing URI such as Influenza A, Rhinovirus and respiratory syncitial virus increases leukotriens levels in nasal secretions. Therefore, one may postulate that leukotriens inhibitors may reduce symptoms during URI. However the effect of montelukast as a treatment for non-specific cough was not properly studied and there are no studies on the effect of montelukast as prevention for URI.

Hypothesis: Prophylactic treatment with Montelukast will reduce the incidence and severity of upper respiratory infection in children.

Inclusion Criteria:

• Children 1 to 5 years old without significant health problem.

Exclusion Criteria:

• A previous history of wheezing (requiring treatment with bronchodilators in the last 3 month or more than one treatment in the last year)
• Hospital admission due to reactive air way disease
• Prophylactic use of montelukast or steroids
• Chronic cardiac or respiratory disease
• Presence of acute respiratory tract infection within the 7 days before consideration for the study
• History of allergic Rhinitis
• Children who are receiving chronic medications of any kind
• Known allergy to montelukast
• Inability to get an informed consent from a legal guardian.