To examine for a relationship between in vivo nonspecific bronchial reactivity to histamine and in vitro smooth muscle response to histamine, we performed inhalation dose-response curves prior to lung surgery in 12 patients and compared this with their bronchial smooth muscle response in vitro. In vivo reactivity was assessed by the provocative concentration of histamine resulting in a 20% fall in forced expiratory volume in one second (PC20), and in vitro reactivity was measured by the negative log of the molar concentration of histamine producing 50% maximal contraction (pD2) as well as maximal tension generated (Tmax). In addition, morphometric analysis was performed on the in vitro tissue to quantitate the amount of smooth muscle present. A wide range of in vivo responses was found in the 12 subjects (PC20-0.065 lead to 16). There was less in vitro variability and no correlation between PC20 and in vitro reactivity assessed by pD20 or Tmax or between PC20 and the percent of smooth muscle.