Asthma is a chronic airway disease with a relatively high prevalence. Although the etiology of asthma is still not fully clear, there are effective treatments available. The treatment strategy for asthma consists of two steps: maintenance therapy with anti-inflammatory agents (inhaled corticosteroids and/or leukotriene antagonists) to reduce airway inflammation and retain proper lung function and secondly, the use of beta-agonists for quick symptomatic relief. Furthermore, oral steroids are used to treat acute exacerbations. There are large differences in response to drug therapy. This may be due to many factors, such as severity and type of disease, compliance, co-morbidity, co-medication (drug-drug interactions), environmental exposures and age. However, calculations of repeatability of treatment response suggest that part of this variance in response to pharmacotherapy could be due to genetic factors. Pharmacogenetics may explain the inter-individual variability in drug response due to genetic variation. Pharmacogenetics is a relatively new emerging research field that provides the opportunity to discover associations between genetic variation and response to a variety of drugs. This review will discuss the pharmacogenetics of antiinflammatory agents (corticosteroids and leukotriene antagonists) used in the treatment of asthma.