An individual's response to anti-asthma medication is likely to arise from a complex interaction between social, environmental and inherited factors. Studies indicate that genetic factors may account for 60-80% of the heterogeneity in treatment responsiveness in asthmatics. Identifying the genetic variants responsible may potentially lead to the development of novel treatments, improved effectiveness in the use of existing treatments and better prediction of efficacy in phase II and III trials. This article will briefly outline the current methods of identifying relevant treatment-responsive genes and their genetic variants. The pharmacogenetics of the main asthma treatment groups will then be reviewed in detail. Finally, the impact of pharmacogenetics on the pharmaceutical industry, and clinical practice in the future will be discussed.