Asthma is the most common respiratory disease encountered in clinical practice, affecting both children and adults. It is an important cause of respiratory morbidity and mortality. Recent therapeutic developments have shown that leukotrienes are the most potent and important inflammatory mediators in the pathology of both acute and chronic asthma. They cause increased bronchoconstriction, mucous secretion, and vascular permeability. Studies using compounds that block leukotrienes (receptor antagonists - montelukast and zafirlukast and 5-lipoxygenase inhibitors - zileuton) have demonstrated improved asthma control in patients aged 12 years and older. In this article we assess the therapeutic importance of these new compounds.