Three hundred and thirty-five patients with bronchial asthma (BA) and 534 patients with chronic obstructive lung disease (COLD) were examined. Before and after tests using salbutamol, phenoterol, ipratropium bromide and a fixed combination of phenoterol and ipratropium bromide, the forced expiratory flow-volume curve was recorded in the patients on each visit (1008 and 1398 visits of patients with BA and COLD, respectively). The study was controlled open-labeled, and prospective. All the bronchodilators were found to be effective in both BA and COLD. However, in asthmatic patients without (less than 4%) and with (more than 5%) eosinophilia, the increase in forced expiratory volume per second (FEV1) was 23.7+/-22.1% and 16.0+/-14.6% of the baseline values, respectively (p < 0.05). Among these patients with ESR of less than 100 mm/hour, the increase in FEV1 was significantly higher--21.7+/-19.7% than in those who had ERS more than 15 mm/hour and this was 13.8+/-17.9% of the baseline values (p < 0.05). Among asthmatic patients, more than 15% increases in FEV1 after administration of bronchodilators were noted in 48% of the patients untreated with inhaled corticosteroids (ICS) and in 61% of the ICS-treated patients (chi2 = 6.55; d.f. = 1; p = 0.01). Among ICS-treated and untreated patients with BA, the mean increase in FEV1 was 24.4+/-22.5% and 19.6+/-22.0% of the baseline values, respectively (p < 0.05). In COLD patients, these differences were absent. It has been concluded that eosinophilic inflammation typical of BA decreases the effect of bronchodilators in BA and that inhaled steroids improve it.