The correlation between proportions of cells in bronchoalveolar lavage (BAL) fluid and ventilatory function was examined in 52 patients with asthma. 1. There was no significant correlation between the proportion of BAL lymphocytes and ventilatory function. 2. The proportion of BAL eosinophils correlated to a certain extent with ventilatory function: the values of %MMF, %V50 and %V25 were lower in patients with BAL eosinophils of 10-19.9% than in those with BAL eosinophils below 4.9%, and %V25 value was significantly lower in patients with a high proportion of BAL eosinophils (10-19.9%) compared with those with a low proportion of BAL eosinophils (0-4.9%). However, ventilatory function was not decreased in patients with BAL eosinophils of more than 20%. 3. The values of ventilatory parameters showed a tendency to decrease with increase in BAL neutrophils. The values of all parameters of obstructive ventilatory dysfunction were significantly lower in patients with BAL neutrophils of > 10% than in those with BAL neutrophils < 4.9%. A significant difference between patients with BAL neutrophils > 10% and < 9.9% was found in values of %V50 and %V25, and the values of %V50 and %V25 were significantly lower in patients with a high proportion of BAL neutrophils (> 10%) than in those with BAL neutrophils < 9.9%. These results suggest that the proportion of BAL eosinophils is to a certain extent related to ventilatory function of asthma patients and that the increase in proportion of BAL neutrophils is closely related to a decrease in values of obstructive ventilatory parameters.