A prospective study has been conducted in an intensive care unit of West Africa in order to determine the clinical and laboratory features of severe acute asthma in black Africans. The study concerned 55 episodes of severe acute asthma, with PaCO2 above 45 mmHg, in 42 patients (26 men and 16 women, mean age 35 +/- 3 years). A triggering factor was found in only 36 percent of the cases. None of the patients were using beta-adrenergic stimulants as maintenance therapy. The mean duration of asthmatic attacks prior to hospitalization was 49 +/- 7 hours. Three patients had cardiorespiratory arrest on admission. Mechanical ventilation was necessary on 12 occasions (initially in 4 and secondarily in 8). Four patients died. It would appear from this study that severe acute asthma in black Africans is characterized by a prolonged onset and by a frequent need for mechanical ventilation, suggesting a physiopathological mechanism different from that described in industrialized countries.