Present evidence suggests that PAF-induced bronchial hyperresponsiveness (BHR) is a variable phenomenon in man. Even in the responders, the magnitude of change is small and the response is poorly reproducible. Endobronchial biopsy and bronchial lavage studies following inhaled PAF did not show any increase in the number of activation of eosinophils, which are pivotal in the pathogenesis of BHR. Unless and until the characteristics of responders are identifiable, PAF inhalation challenge should not be used as a human model of BHR.