Leukotrienes (LTs), in particular LTC4, LTD4, and LTE4, have been shown to be capable of participating in the induction of three related processes observed during the immediate reaction in bronchial asthma: edema formation, mucus secretion, and muscle contraction. Despite impressive evidence potentially implicating the LTs, the role of LTs in asthma is still unproved, and a positive answer to their critical actions in causing airflow obstruction will require studies with specific antagonists.