Asthmatic patients who came to hospital for treatment of severe attacks were assessed for level of obstruction and the effects of a deep inhalation (DI) on degree of obstruction at various stages of their treatment and after recovery over several days. The more severe the obstruction, the greater was the constrictor effect of a DI; as lung function improved with intensive treatment, including corticosteroids, the constrictor effect diminished. Thus, we believe the constrictor effects of a DI relate to the degree of inflammation in the obstructive process. These longitudinal data relating severity to the effects of a DI were nearly identical to previously published cross-sectional data in a group of patients with spontaneous asthma with widely different levels of lung function. It is possible that the response to a DI in a given asthmatic subject serves as a functional marker for the predominant mechanism for obstruction.