HQL-79 is a selective inhibitor of hematopoietic PGD synthase. Structurally, it is a synthetic tetrazole compound originally prepared as a possible antihistamine.{11338} Subsequent evaluation in models of allergy and asthma demonstrates the HQL-79 is orally available, and inhibits the synthesis of PGD2 (Item No. 12010).{11337} HQL-79 is thus a likely lead compound for the preparation of potent, selective hematopoietic PGD synthase inhibitors.