Sulukast (also known as LY170680 ) is an antagonist of the cysteinyl leukotrienes C4, D4, E4 patented by Lilly Industries Ltd. for the treatment of asthma. In vitro, Sulukast was a potent, selective, and competitive antagonist of LTD4, and LTE4. It produced a concentration-dependent rightward displacement of the concentration-response curves elicited by either LTD4 or LTE4 on both the guinea-pig ileal and tracheal preparation. Intravenous Sulukast reduced in a dose-dependent manner the fall in compliance in the anesthetized guinea-pig, and the rise in total pulmonary resistance. Sulukast was also effective in reducing the increase in total pulmonary resistance to intravenous antigen in sensitized animals pretreated with mepyramine, indomethacin, and propranolol. Inhaled Sulukast was particularly effective in preventing the increase in total pulmonary resistance produced by exposure to aerosolized LTD4.