Double-blind cross-over studies of oral and inhaled terbutaline and salbutamol have been performed in two groups of asthmatic patients. Both drugs at the doses recommended by the manufacturers produced similar maximal effects. The onset of response was faster with inhaled treatment and there was no difference in length of action between the drugs or the routes of administration. Side-effects were much more common with oral treatment. In a separate study oral and inhaled terbutaline were compared in 11 asthmatic patients and this also showed a similar maximal response in tests of forced expiration. A greater response was seen in sGaw following inhaled treatment (P less than 0.05). These results suggest that beta-2-sympathomimetic drugs should be administered by the inhaled in preference to the oral route.