Ebastine is a novel histamine H1 receptor antagonist that combines potency with a rapid onset (fast absorption) and long duration (slow elimination) of action, at least partially mediated via the formation of an acid metabolite (carebastine) that is even more potent as an antihistamine. It shows clear selectivity for histamine H1 as opposed to H2 receptors, has moderate activity against other potential mediators of allergic phenomena such as leukotriene C4 and platelet-activating factor, and is clearly effective against anaphylactic reactions resulting from exposure of suitably sensitised tissues or animals to antigen. By contrast, ebastine has negligible activity against acetylcholine (no atropine-like adverse effects on secretions and visual accommodation) and only poorly penetrates the blood-brain barrier (no sedative adverse effects). Ebastine is without effects on the central nervous and cardiovascular systems, even after oral administration of high doses, and does not interact pharmacologically with a wide range of other drugs covering most areas of potential coadministration. Furthermore, ebastine showed no clinically relevant effects in a complete set of regulatory-required toxicity tests (including acute, chronic, reproductive, mutagenic and carcinogenic protocols) at doses giving blood concentrations representing high multiples of clinical exposure. In conclusion, ebastine has a preclinical profile indicative of an excellent therapeutic ratio of desired effects to undesired effects.