OBJECTIVE To familiarize readers with a potentially new class of compounds for treating asthma. Background information on leukotrienes is provided in addition to an in-depth review of pertinent clinical trials. METHODS Information was obtained from controlled clinical trials, abstracts, and review articles identified through a MEDLINE search of English-language articles. METHODS Emphasis was placed on early clinical trials that showed some benefit with these compounds as well as more recent studies using newer agents that produced more promising results. METHODS Information regarding leukotriene biochemistry was extracted from basic science research and data from human studies were evaluated by the authors according to patient selection, study design, methodology, and therapeutic response. RESULTS Leukotrienes have a pathophysiologic role in asthma. Two distinct but pharmacologically similar classes of leukotriene inhibitors are currently being clinically evaluated. These are leukotriene receptor antagonists and 5-lipoxygenase inhibitors. Early clinical trials with these agents yielded unfavorable results primarily because of lack of drug potency and selectivity, poor patient tolerance, and possibly the route of administration. Subsequent studies with more potent and selective agents have further implicated leukotrienes as biochemical mediators in asthma and, consequently, have shown promising clinical outcomes with respect to pulmonary function testing and patient tolerance. CONCLUSIONS Advancements in the pathogenesis of asthma are beginning to define a role for the leukotrienes. Although more studies are needed to assess the efficacy of leukotriene inhibitors, recent clinical trials using leukotriene-receptor antagonists and 5-lipoxygenase inhibitors indicate a potential for the expansion of therapeutic regimens currently used in the treatment of asthma.