With cloning of the gene encoding the histamine H₁ receptor, a new area of histamine research has become reality. Finally, it seems feasible to study the target of the thera‐peutically important clans of antihistamine. Expression of the genes in mammalian cells allows detailed investigations of the various signal transduction routes of the histamine H₁ receptor. Moreover, using molecular biological techniques, it is now possible to investigate ligand receptor interaction at the molecular level. Studies with mutant H₁ receptors have shown that H₁ antagonists bind to a specific amino acid residues in TM3 and 5. It is expected that these new developments will provide much fundamental knowledge on the ligand interaction with the H₁ receptor.