Primary Human Tracheal Smooth Muscle Cells (HTSMC) are isolated from the trachea from single donors and stain positive for smooth muscle α-actin. They connect the endings of the tracheal cartilage by a contractile bridge called the paries membranaceus and consequently regulate the airway lumen. Under pathological conditions like asthma, the amount of smooth muscle cells in the trachea walls is increased leading to smooth muscle hypertrophy or hyperplasia. Hence, HTSMC are suitable for in vitro studies of asthma and other pulmonary diseases.