One main area of pharmacogenomics is the discovery of new drugs and drug targets with molecular genetic or genomic methods; the other is the study of how genomic differences influence the variability in patients responses to drugs. In this review the authors summarise the most important results of this latter issue. Despite the availability of three major classes of therapeutic agents for asthma, it has been estimated that as many as half of asthmatic patients do not respond to treatment with beta2-agonists, leukotriene modifiers or inhaled corticosteroids. Moreover, in some individuals asthma therapy has been associated with serious adverse drug reactions. An estimated 60 to 80% of variability in individual responses to therapy may have genetic bases. All of the currently available data on asthma pharmacogenomics originated from genetic variations in genes of the drug treatment target or target pathways. Results of genetic association studies that investigate responses to beta2-agonist, leukotriene modifier and corticosteroid therapy will be summarised and recent findings in the literature highlighted. Although, at present pharmacogenomics can explain only a fraction of the adverse drug responses, hopefully these results mark the clinical use of genotyping at an individual level as adjunct to pharmacotherapy for asthma and many other diseases.