The speed of onset of an asthma attack can be highly variable. Recent studies have tried to characterize a subgroup of patients with life-threatening asthma that occurs suddenly but often regresses very rapidly under treatment. We had the opportunity to observe the evolution of two asthmatic women hospitalized with extremely severe respiratory acidosis. One of them required immediate orotracheal intubation and mechanical ventilation during 13 h. The results of her pulmonary function tests were normal 35 h after admission. The second woman's condition improved so rapidly under treatment that she did not require intubation and mechanical ventilation. These observations suggest that bronchospasm might play an important role in the pathophysiology of transient life-threatening asthma.