Airway smooth muscle is fundamental for maintaining airway tone. The specialized ultrastructural features and regulatory mechanisms of airway smooth muscle are vital for normal airway function. Patients with respiratory disorders, such as severe asthma, exhibit the distinguishing feature of increased bronchial smooth muscle mass. The increase in smooth muscle mass is related either to abnormal bronchial smooth muscle cell (BSMC) proliferation or the accumulation of contractile protein. Smooth muscle cell proliferation is an important component of airway remodeling in asthma. It is consequently a target for the development of novel anti-asthma agents. Airway smooth muscle cells express CT-1 and release GM-CSF, RANTES and IL-8 in vitro. In order to develop therapies for asthma, researchers have utilized Human Bronchial Smooth Muscle Cells to elucidate the cellular and molecular mechanisms underlying BSMC proliferation.