The beta(2)-adrenergic receptor (beta(2)AR) is the molecular target for beta-agonists used in the treatment of asthma. In the human population, 4 polymorphisms of the beta(2)AR coding block have been found, 3 of which result in receptors that have different properties compared with wild-type. To date, clinical studies suggest that these beta(2)AR polymorphisms may alter asthmatic phenotype and the response to beta-agonist therapy, making these variants the first of undoubtedly several genetic loci that will ultimately be found that will provide for individualized therapy in asthma.