Leukotrienes are metabolites of arachidonic acid catalyzed by a novel lipoxygenase specific for the C-5 position. These fatty acids have many pharmacological properties including smooth muscle contractions and leukocytes activation, and are believed to play a key role in inflammatory and hypersensitivity reactions. Experimental evidence suggests that the action of leukotrienes is mediated by specific receptors. In this paper pharmacological and biochemical data in favor of the existence of leukotriene receptors are presented and hypotheses on the mechanisms of action and transduction are discussed.