Study design is shown with an example. Increasing concentrations of methacholine (0.04, 0.08, 0.16, 0.31, 0.63, 1.25, 2.5, 5, 10, 20, 40, 80, and 160 mg/ml) were inhaled until a fall of 20% or more in FEV1(PC20-FEV1) from the post-saline value occurred. After each concentration of methacholine inhalation, partial and full flow-volume curves were measured. Coughs were counted for 2 min during the inhalation and for 30 min following the inhalation of methacholine at PC20-FEV1. [(a) In this case].