Despite the widespread use of inhaled corticosteroids, many asthmatic patients experience persistent symptoms. In such individuals, the addition of a long-acting β2-agonist (LABA) is frequently more effective than doubling the dose of inhaled corticosteroid. However, the role of additional therapy with a leukotriene receptor antagonist (LTRA) as an alternative to an LABA has been the focus of attention in recent studies. In order to determine the overall efficacy of the pharmacologic armamentarium used in asthma, it is imperative that a combination of end points, including lung function, airway hyperresponsiveness, effects on underlying inflammation, symptoms, and more long-term sequelae such as exacerbations, are assessed. This evidence-based systematic review outlines the pharmacologic properties of LABAs and LTRAs and the importance of evaluating end points in addition to lung function when assessing these drugs. We also highlight the results of all published studies that have performed direct comparisons of both LABAs and LTRAs as add-on therapy to inhaled corticosteroids.