Histamine receptor family consists of four members, namely, H1, H2, H3, and H4. The histamine H4 receptor is the most recently identified G protein-coupled histamine receptor that binds to several neuroactive drugs, including amitriptyline and clozapine. So far, H4 receptors have been found only on haematopoietic cells. This signifies its important role as a drug target for the trea™ent of inflammatory diseases.