Ten subjects with various degrees of asthma severity underwent a three-day trial, with the aim of evaluating the bronchodilating effect of inhaled formoterol (12 micro g), in comparison with salbutamol (200 micro g) and salmeterol (50 micro g). The bronchodilation afforded by formoterol paralleled that of salbutamol in rapidity (mean percentage increases in functional measurements (FEV(1)) vs. baseline recorded 5 min after drug administration: 7.7%, 9.3%, and 0.3% for salbutamol, formoterol and salmeterol, respectively) and that of salmeterol in duration (mean percentage increases in FEV(1) vs. baseline recorded 12h after drug administration: 16.8% and 15.9% for formoterol and salmeterol, respectively). Moreover, the maximal effect of formoterol resulted to be slightly higher in comparison with salbutamol (P<0.001) and salmeterol (P<0.05); in this regard, the mean percentage increases in FEV(1) vs. baseline recorded 2h after salbutamol and formoterol, and 4h after salmeterol were 22.3%, 29.5%, and 24.6%, respectively. Therefore, these results suggest that formoterol can be used, in addition to its utilization as long-acting bronchodilator, also as an effective rescue medication for the immediate relief of asthma symptoms.