SummaryVarious mediator systems have been stressed as important in the generation of the signs and symptoms of allergic disease such as hay fever. Nevertheless, in the upper airways, histamine is still the only mediator which behaves consistently in terms of release at appropriate challenge, produces all the major symptoms of rhinitis at a local challenge, and the specific antagonist influences the signs and symptoms of rhinitis in the challenge situation as well as during natural allergen exposure. Although the majority of hay fever symptoms are influenced by H1‐receptors, there are exceptions. An important one is the symptom of nasal blockage, which is due to tissue oedema and a decrease in the tone of the capacitance vessels. Another point to be stressed is that histamine alone does not induce any protracted mucosal inflammatory response with associated symptoms, influx of eosinophils and increase in responsiveness that is associated with the exposure to allergen. Nevertheless, from a clinical point of view, antihistamines are still valuable pharmacological agents for the clinical management of hay fever symptom
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