Histamine plays a prominent and diverse role in the pathophysiology of allergic disease and therapeutic intervention is therefore typically focused on blocking the effects of this biogenic amine. A new antihistamine, levocetirizine, is the R-enantiomer of cetirizine dihydrochloride and like its parent compound undergoes minimal hepatic metabolism. Levocetirizine has pharmacodynamically and pharmacokinetically favourable characteristics, including high bioavailability, rapid onset of action, limited distribution and a low degree of metabolism. Clinical trials indicate that it is safe and effective for the treatment of allergic rhinitis and chronic urticaria with a minimal number of untoward effects. Furthermore, several recent studies have demonstrated that, in addition to its being a potent antihistamine, levocetirizine has several anti-inflammatory effects that are observed at clinically relevant concentrations that may enhance its therapeutic benefit.