Pharmacogenetic approaches provide the opportunity to improve prescribing for asthmatic patients in order to optimise efficacy and prevent side-effects. Currently, there are comprehensive data available on the extent of genetic variation in the human genome that will further this area of research. However, less is known about the functional consequences of many of the identified polymorphisms in genes whose products may predict drug efficacy. In addition, there is a shortage of well-designed, adequately powered clinical studies in this area. This series summarises the current state of knowledge and identifies areas for further research.