The effect of suggestion on the airway response to 10 inhalations of normal saline followed by doubling concentrations of isoproterenol was assessed in 12 normal and 30 asthmatic subjects. It was suggested that the first 5 saline solutions contained a bronchoconstrictor and that the second 5 contained a bronchodilator, or vice versa, and that the first 4 isoproterenol solutions were inert, whereas the last was a bronchodilator. Nine asthmatic, but no normal subjects, bronchoconstricted after saline inhalation, with a mean fall in specific airway conductance (SGaw) of 40%. This was dose-dependent and was abolished when inhalations were carried out at 37 degrees C 100% relative humidity. Suggestion did not affect the airway response to saline or isoproterenol in either group, but it did influence the subjective impression of airway caliber recorded on a visual analogue scale. In this study, the bronchoconstriction after saline inhalation, previously attributed to the effect of suggestion, was caused by airway cooling.