Primary Human Bronchial Smooth Muscle Cells (HBSMC) are isolated from the bronchi from single donors and stain positive for smooth muscle α-actin. They connect the endings of the bronchial cartilage and consequently regulate the airway lumen. Under pathological conditions like asthma, the amount of smooth muscle cells in the bronchi walls is increased leading to smooth muscle hypertrophy or hyperplasia. Hence, HBSMC are suitable for in vitro studies of asthma and other pulmonary diseases.