The present invention provides a method of determining the susceptibility of a subject to treatment with a leukotriene modifier by determining the subject's cysteinyl leukotriene (CysLT) level and the subject's level of eosinophilic airway inflammation and identifying a subject with a high ratio of CysLT levels to eosinophilic airway inflammation as susceptible to treatment with the leukotriene modifier. Also discussed is a method of treatment of subjects who are susceptible to treatment that includes administering a leukotriene modifier to such a subject.