A double blind study of 5 asthmatic subjects in remission demonstrated that the severity of bronchoconstriction after exercise was decreased by a single oral dose of 5 mg of terbutaline. The effect lasted for at least 6 hours and was significantly better than the protection afforded by 20 mg of metaproterenol, which was itself more effective than a placebo. In these doses, neither terbutaline nor metaproterenol affected heart rate or blood pressure at rest or in exercise, and no drug-induced side effects were found.