Carbuterol is a beta-adrenergic bronchodilator with selectivity for bronchial smooth muscle relative to cardiac and vascular tissues of several species including man. In vitro studies demonstrated that carbuterol was a direct acting beta-adrenergic agonist, not dependent on endogenous catecholamine release, and was devoid of alpha-adrenergic agonist activity. The activity of the racemate was shown to reside primarily in the l-enantiomer. Carbuterol inhibited immunologically induced release of histamine and slow reacting substance of anaphylaxis from passively sensitized fragmented rhesus monkey lung and also inhibited passive cutaneous anaphylaxis in rats. Acute toxicity studies in mice, rats and guinea pigs indicated a wide safety margin for carbuterol. Carbuterol is a safer and more effective bronchodilator than ephedrine.