In passively sensitized guinea pigs, show infusion of an amount of ovalbumin insufficient to evoke airway obstruction induces hyperreactivity of the airways. A wide range of changed responsivity was observed for different test spasmogens, with leukotriene C4 > histamine > prostaglandin F2 alpha > bradykinin > leukotriene E4 > serotonin > acetylcholine. Injection of ovalbumin as a bolus produced pronounced airway obstruction without hyperreactivity. Airway obstruction due to vascular engorgement (dextran infusion) or edema (histamine infusion) did not result in hyperreactivity. Infusion of PAF induced pronounced airway obstruction together with hyperreactivity, but with a rank order of histamine > leukotriene C4 > serotonin > bradykinin > leukotriene E4 > acetylcholine. It can be concluded that allergic airway hyperreactivity in the guinea pig is spasmogen-selective and largely independent of airway obstruction. These observations question the presumption of non-selective hyperreactivity in allergic asthma and cast doubt upon the proposal that airway hyperreactivity is secondary to airway obstruction.