Inhaled short-acting b2-agonists (SABA) are the most potent bronchodilators used today to treat acute symptoms of asthma and albuterol, a partial b2-agonist, is the most frequently prescribed asthma medication in the US. Although universally used in for acute asthma symptoms, SABA have been associated with a significant degree of interpatient variability. Many studies have characterized the SABA dose to bronchodilator response relationship under controlled conditions. However, few studies have explored the magnitude and sources of bronchodilator response variability, and no studies have characterized the dose versus bronchodilator response relationship using population pharmacokinetic/pharmacodynamic (PPK/PD) modeling. In the present study, we characterized the relationship between inhaled doses of albuterol and bronchodilation in 81 children and adults with moderate to severe persistent asthma using a population pharmacodynamic approach. The purpose of this study was to obtain estimates of the pharmacodynamic parameters that characterize the dose-response curve, including maximal dose for bronchodilation, and to quantify and identify sources of interpatient pharmacodynamic variability.