Dametralast is an antihistamine agent. Bronchodilator action of dametralast was demonstrated on the isolated trachea of guinea pigs. Dametralast prevents bronchospasm in anesthetized guinea-pigs, protects mice from anaphylactic shock induced by injection of bovine albumin, and has a protective effect in passive cutaneous anaphylaxis test in rats. Investigations into the mechanism of action have shown that the drug was ineffective on the synthesis of cyclooxygenase products from arachidonic acid. Dametralast inhibited cAMP phosphodiesterase (PDE) but this inhibition does not seem to be involved in their anti-inflammatory activity. In clinical tests dametralast was well tolerated; functional respiratory exploration determinations provided the same bronchodilator effect found in animals. A favorable effect was noted in asthmatic subjects and in subjects suffering from respiratory insufficiency.