Very little is known as yet about the effect of salmeterol in pediatric asthma, so a trial was performed on children with mild asthma to compare salmeterol with salbutamol in terms of how quickly they took effect. The double-blind study involved 11 children (mean age 13.4 years) randomly assigned to inhale salmeterol 50 micrograms, salbutamol 200 micrograms, or a placebo three times on alternate days. Peak expiratory flow (PEF), heart rate, and blood pressure were measured before and 5, 10, 15, and 20 min after administering the medication. With salbutamol, PEF was higher at 5 and 10 min, subsequently dropping off at 15 and 20 min; with salmeterol, PEF was better at 10 and 20 min. Forced expiratory volume at 1 s (FEV1) measurements taken at the baseline and after 10 and 20 min revealed an important and consistent rise in values after salmeterol, whereas salbutamol was more effective after 10 min than after 20 min. No significant changes were recorded in heart rate or blood pressure after salbutamol; after salmeterol, there was a significant increase in heart rate after 5 min, but not at subsequent measurements. In conclusion, salmeterol begins to take effect already within 10 min of a single administration in asthmatic children, although the onset of its effect is slower than with salbutamol.