Bitolterol, (3-4 diester colterol) is a new beta 2-adrenergic agonist. Since it in itself is biologically inactive, bitolterol is considered a pro-drug. When administered it is activated within the lung by esterase hydrolysis to the active compound colterol catecholamine N-t-butyl-arterenol). In preclinical and clinical studies to date, bitolterol has proved to be an effective bronchodilator for adult and pediatric patients with chronic stable asthma and for some with chronic obstructive pulmonary disease. Bitolterol has been compared with other beta 2 agents, including isoproterenol, metaproterenol and albuterol. There is no evidence for cardiotoxicity when bitolterol is used in combination with theophylline in human studies. It is effective for control of exercise-induced asthma.