The bronchodilator effects of inhaled fenoterol (FI) and salbutamol aerosol (S) in 15 patients (8 male and 7 female with a median age of 44 +/- 13 years), diagnosed as suffering from asthma, were studied using spirometry (determining FEV1, FEF 25-75% and FVC) and flow volume curves (PEF, MEF 75% and MEF 25%). The mean theroric rate of FEV1, PEF, MEF 75% was defined as the theoric rate of the obstruction of central airways (PCA%) and the mean of FVC, FEF 25-75% and MEF 25% rates defined as the rate of the theoric obstruction of the peripheral airways (PPA%). Basal and 5, 15, 30, 60, 120, 240, 360, 480 minute determinations were done, after the administration of 200 mcg of S in the conventional way on two different days. The statistic study carried out using the "u" test of Mann-Whytney. No statistically significant differences in intensity, onset nor duration of the effect between both drugs were found. We concluded that FI is a drug of great utility in treatment of asthmatic patients and one which allowed, because of the easy inhaling technique, the use of beta 2 adrenergic drugs in a mayor number of patients who would otherwise have to resort to an alternative form of administration.