Tiprinast (MJ 12175) is one of a series of thienopyrimidine-carboxylic acids synthesized as possible antiallergy compounds. In clinical studies it has been shown to be efficacious in preventing the symptoms of ragweed hay fever when used as a nasal spray. Tiprinast has been shown to resemble disodium cromoglycate (cromolyn) in biologic activity in a variety of antigen-induced allergic test systems. Both compounds inhibit passive cutaneous anaphylaxis in the rat, histamine release from rat peritoneal mast cells and nasal constriction due to antigen in the rat. In all cases tiprinast is more potent than cromolyn and also longer acting. Tiprinast, like cromolyn, appears to elicit a cardiac reflex (Bezold-Jarisch) in the anesthetized dog.