A potent and selective histamine H4 receptor antagonist, with a Ki value of approximately 4 nM against the human, mouse, and rat H4 receptors; inhibits mast cell chemotaxis induced by 10 μM histamine (IC50 = 40 nM), reduces neutrophil influx in mouse peritonitis models (10 mg/kg s.c.), and impairs eosinophil and lymphocyte influx into airways during allergic airway inflammation.