Beta-adrenergic receptor agonists are critical in the treatment of asthma. Their use frequently results in effective bronchodilation. Commonly used beta-adrenergic agonists are epinephrine, albuterol and terbutaline, with albuterol and terbutaline having an increased selectivity for beta-2 receptors. These agents can be given by inhaled, IV, subcutaneous or oral routes. In the United States inhaled albuterol is the drug and route of choice in a majority of circumstances. Regarding efficacy when administering medications via the inhaled route, one must take into account many factors including inhalation technique, inspiratory flow rate, inspiratory volume and mode of delivery. Several characteristic pathophysiological changes that occur during a severe asthma attack (near complete airway obstruction, low tidal volumes, mucus plugging) may preclude the delivery of inhaled particles to the area of the lung that is most affected. In these instances, intravenous beta-agonists should be considered. Because of cardiac related side effects that are more pronounced in non-selective beta-agonist therapy, a beta-2 receptor agonist should be administered. In the United States, terbutaline is the only approved intravenous beta-2 receptor agonist.