Responses of human bronchial strip preparations to contractile and relaxant agonists were measured in preparations from non-diseased and from asthmatic lung obtained 3-15 h post-mortem. The potencies of carbachol and histamine were approximately two times less in asthmatic than in non-diseased bronchi. This was statistically significant for carbachol (P less than 0.05), but not for histamine (P greater than 0.05). These results clearly indicate that the bronchial hyperreactivity to airway spasmogens observed in asthma is exclusively an in vivo phenomenon not involving increasing sensitivity of bronchial smooth muscle. The potencies of the beta-adrenoceptor agonists isoprenaline, fenoterol and terbutaline were significantly reduced by 4-5 fold in asthmatic bronchi compared with non-diseased airways. In contrast, theophylline was equipotent in the two populations of airway preparations. Thus, it appears that severe asthma is associated with decreased bronchial smooth muscle beta 2-adrenoceptor function.