||BACKGROUND: Determining who responds to asthma therapies, particularly leukotriene modifiers, continues to be explored. OBJECTIVE: We sought to identify patient characteristics predictive of response to montelukast. METHODS: We used data from 2 clinical trials in which children with asthma received either montelukast or placebo. Symptoms, beta-agonist use, and unanticipated health resource use caused by asthma were recorded in validated daily diaries for children 2 to 5 (n = 689) and 6 to 14 (n = 336) years old. We defined primary end points of days without asthma in 2- to 5-year-old patients (24 hours without symptoms, beta-agonist use, or asthma attack) and change in percent predicted FEV(1) in 6- to 14-year-old children. Asthma attack was defined by the use of rescue oral corticosteroids or by an unscheduled visit to a medical provider. Patients were grouped according to baseline characteristics, such as family history of asthma, personal history of allergy, frequency of asthma symptoms, eosinophilia, and concomitant use of inhaled corticosteroids or cromolyn. We examined the stratum-specific effects of montelukast on the percentage of days without asthma, change in percent predicted FEV(1), asthma attack, and a variety of secondary symptom and FEV(1) end points. RESULTS: We did not identify characteristics that predicted response to montelukast in either preschool or 6- to 14-year-old children. These findings were consistent across all symptom and FEV(1) outcomes. There was also no differential response to montelukast in either age group when asthma attack was the outcome. CONCLUSION: The patient characteristics studied do not appear to provide an indication of who will benefit most from treatment with montelukast.