A double-blind, cross-over protocol was applied to 22 asthmatic patients who were previously subjected to provocation tests with methacholine. The baseline FEV1 for mild asthma was 89.6 +/- 13.6% while for moderate asthma it was 73 +/- 6%. The initial provocation tests with methacholine revealed that the mild asthma group needed a greater accumulated dose of methacholine than that required by the moderate asthma group to lower the FEV1 by 20%, stressing the enhanced bronchial hyperreactivity present in the latter group. Significant differences in the PD20 values were obtained in both groups of patients using the combination of salbutamol plus beclomethasone. Salbutamol alone was ineffective to change the PD20 values in mild asthma while beclomethasone alone was able to change significantly the PD20 values in these patients, stressing the importance of the inflammatory component in the pathogenesis of stable asthma. Furthermore, the combination of both drugs was also more effective in the moderate asthma group than either medication alone, confirming the pharmacological control of the obstructive and inflammatory changes that are already established in patients with moderate asthma.