Following the sequencing of the human genome, data-mining efforts have revealed the existence of a new histamine receptor that is expressed at high levels in mast cells and leukocytes. The histamine H(4) receptor has a distinct pharmacological profile and the first compounds that act selectively on the H(4) receptor have been developed. Initial experiments in vivo with H(4) receptor antagonists indicate a role for the H(4) receptor in inflammatory conditions.