The present invention provides a new analytical method for measuring leukotrienes in a clinical sample using liquid chromatography and tandem mass spectrometry (LCMSMS). The method provides a simple, rapid and low-cost assay for the measurement of leukotriene levels in a clinical sample with high accuracy and precision over the physiological range. The present invention further provides a method to determine the susceptibility of a subject to treatment with a leukotriene modifier, as wells as methods for diagnosis of a chronic obstructive disease of the airways and for predicting the risk of exacerbation of the same.