The antileukotriene agents are the first new category of asthma medications introduced in the past two decades. Leukotriene synthesis inhibitors block the production of leukotrienes whereas leukotriene receptor antagonists block the effects of leukotrienes at the receptor level. Leukotriene synthesis inhibitors are further classified as either 5-lipoxygenase inhibitors or 5-lipoxygenase-activating protein inhibitors. Zafirlukast, montelukast, and pranlukast are leukotriene receptor antagonists whereas zileuton is a 5-lipoxygenase inhibitor. Antileukotrienes have been shown to be relatively safe and effective in chronic mild to moderate asthma. Studies are ongoing to determine how they compare with inhaled steroids, which remain the drug of choice for anti-inflammatory therapy.