Sixteen subjects with mild stable asthma participated in a randomized double blind study on the effects of low dose fenoterol against histamine induced bronchoconstriction. Fenoterol aerosol at concentrations of 10, 50 and 200 μg and placebo were delivered at random through a metered dose inhaler as a single dose 30 min before histamine challenges on four separate occasions. Compared to placebo a fenoterol dose of 10 μg provided significant bronchodilatation (sRaw [s.d.] 8.3 [2.73] vs 6.3 [1.74] cm H20 * s [P<0.05]) and protection (PC100 sRaw [s.e.m.] 0.72 (1.31) vs 1.45 (1.39) mg/ml). The bronchodilatory and protective actions of fenoterol were more pronounced after the inhalation of 200 μg (P < 0.05) with no difference between 10 and 50 μg fenoterol aerosol. The magnitude of bronchodilatation and protection was not correlated (r= 0.15). The results from this acute study may suggest that fenoterol at doses up to 20 times lower than routinely recommended may be an effective treatment in mild asthmatics.