There is great interindividual variability in the response to asthma medications, and a substantial portion of this variability has a genetic basis. Pharmacogenomics is a rapidly evolving discipline and approach to patient care that uses genetic information and genomic technologies to identify underlying mechanisms that are responsible for these variable therapeutic responses. In this article, the pharmacogenetic principles in the context of asthma are described. Several examples of polymorphisms in genes that impact the efficacy of beta(2)-agonists and antileukotriene drugs have been identified and are discussed. Analysis of polymorphisms likely is to be used routinely in clinical practice for optimizing asthma drug therapy.