We investigated the effect of inhalation of cotton bract extract (CBE) on bronchial responsiveness to methacholine. Thirteen (13) healthy volunteers were exposed to CBE or SHAM (normal saline) in a double-blind, random, cross-over fashion with measurements of non-specific bronchial responsiveness prior to and 2 and 8 hours following provocation. For the group, mild and transient airway hyperresponsiveness developed (P < 0.05) and these changes were not dependent on the severity of CBE-induced changes in flow-volume parameters.