The effects of tartrazine on the synthesis of prostaglandin-like substances (PGLS) from arachidonic acid in isolated perfused guinea pig lung, and on the contractile responses of guinea pig tracheal tissues induced by histamine, acetyl-choline, bradykinin, serotonin and prostaglandin F_2α were studied. The synthesis of PGLS from arachidonic acid was not inhibited by tartrazine. The contractile responses of guinea pig tracheal tissues induced by various bronchoconstrictors were potentiated in the presence of tartrazine. These results may suggest that tartrazine-induced asthma is not induced by inhibition of PGLS synthesis, but induced by potentiation of bronchoconstrictor responses.