Only a small number of studies investigating the in vitro pharmacologic properties of airway smooth muscle in asthma and well-characterized COPD have been performed. Further detailed studies on well-defined patient groups are required. The majority of available evidence would suggest that once airway smooth muscle is removed from its in vivo milieu, it loses the characteristics of hyperresponsiveness. This would explain why there are no clear differences in the pharmacologic responsiveness of tissue from patients with asthma or COPD and those with no obstructive disease. Future in vitro studies should be directed towards reproducing the in vivo environment. this would entail the establishment of a chronic inflammatory condition created by the continuous presence of neural and humoral factors.