The beta 2 adrenoceptor has been cloned and sequenced, and details of how agonist stimulation ultimately results in clinically evident effects are now known. Receptor desensitization by agonist is an almost universal process that can be prevented and reversed by corticosteroids. Although immunologic mechanisms appear to prevail in asthma, beta 2 receptor dysfunction may be important in some circumstances. Many receptor agonists are available for asthma therapy, including a new generation of long acting agents (such as salmeterol) with duration of action of 12 hours or more. Statistical links between beta agonist use and asthma mortality or morbidity warrant careful examination for clinical relevance, but may not be dismissed. Beta agonists are relatively safe and clearly effective in asthma, but anti-inflammatory management (including allergen avoidance and immunotherapy when appropriate) is indicated in patients who require chronic therapy.