Patients during a mild to moderate acute attack of asthma (FEV1: 50 -80% of predicted) were treated with Salmeterol MDI -50mcg or Rotadisk -50mcg or Salbutamol (MDI200mcg). The children were followed by Spirometry, measuring FEV1 (basal) and after treatment: at 30 minutes, 60 minutes and thereafter every 60 minutes until 780 minutes, if the patients mantained the FEV1 above 80% of the predicted value and/or an increment of 20% in the VEF1 basal value. The Salmeterol group showed a significant bronchodilation at 60 minutes which was maintained in half of the patients up to 9 hours. This was not observed in the Salbutamol group: the peak bronchodilatation was observed at 30 minutes and the bronchodilation effect was observed in half of the patients up to 6 hours. There were no significant differences between both presentations of Salmeterol. This drug allowed a prolonged bronchodilator effect and is, according to the several consensus on management of asthma, an adequate option in the treatment of moderate to severe asthma.