There is good evidence to suggest that the late response is a valid clinical model of asthma. The factors which predict late responses in individual subjects are unknown although recent studies suggest that the level of IgE sensitivity and allergen dose are two important variables. Recent placebo-controlled phamacological studies support earlier work and vindicate the use of late responses as a preclinical screening test in the evaluation of new therapeutic agents. In addition to putative pro-inflammatory mechanisms we should evaluate possible protective mechanisms which might prevent the development of late responses in individual subjects. In this regard, altered adrenal responses as reflected by serum cortisol concentrations did not appear to play a role, protective or otherwise in the development of late asthmatic responses [49](Fig. 2). In conclusion, the development of symptomatic late responses and associated increased bronchial responsiveness are relevant to day-to-day asthma. As suggested by Cockcroft [50], repeated allergen exposure may result in a vicious cycle of ongoing bronchial inflammation. This emphasizes the importance of allergen avoidance and the need for earlier intervention in mild to moderate asthma with effective prophylactic agents which are known to inhibit late responses.