Ventilatory function was compared between two age-matched asthma groups : group A (study group) consists of 8 patients with bronchial asthma with marked neutrophilia (20% or more) in the BAL fluid and group B (control group) of 8 patients with neutrophils (less than 5% of total BAL cells). The values of six ventilatory parameters were lower in group A than in group B, and a significant difference was found in FEV(1.0%), % MMF, % V(50) and % V(25) between groups A and B. Of these parameters, the value of % V(25) was markedly decreased in group A compared with group B. The results show that ventilatory dysfunction in airways, especially in small airways, is closely correlated to increased number of neutrophils in BAL fluid.