Asthma is characterized by airway hyperreactivity, an abnormal tendency for airways to constrict. Maternal asthma increases the risk of childhood asthma more than paternal disease, suggesting intrauterine exposures contribute to airway hyperreactivity. As airway hyperreactivity seldom returns to the normal range despite intensive treatment, this suggests that structural alterations with in utero origins impair lung function lifelong. I hypothesized that airway hyperreactivity in offspring born to mothers with asthma is established during development and results from increased lung sensory innervation.