A number of reports have characterized cetirizine as a potent histamine H1-receptor antagonist possessing inhibitory effects on eosinophil chemotaxis. In clinical pharmacological tests, cetirizine markedly reduced wheal and flare responses induced by histamines. The inhibition was fast onset, potent and long-lasting. A single clinical dose of cetirizine was more potent in inhibiting wheal response than other antihistamines such as terfenadine, loratadine, epinastine and ebastine. Cetirizine also inhibited eosinophil chemotaxis in vitro at a concentration easily attained after a clinical dose of 10 mg. Eosinophil infiltration into a site challenged with allergen in vivo was also inhibited. Potent antihistaminic effects of cetirizine afforded fast and strong relief from histamine-induced symptoms such as sneezing and rhinorrhoea in allergic rhinitis and itchy sensation in idiopathic chronic urticaria. Inhibitory effect of cetirizine on eosinophil chemotaxis may alleviate minimal persistent inflammation due to faintly but repeated intake of allergen. Such anti-inflammatory properties of cetirizine may be beneficial in reducing hypersensitivity to normalize the upper respiratory tract and eosinophil-related skin inflammation.