Leukotrienes are potent mediators of allergy and inflammation. Polymorphonuclear granulocytes which participate in acute and chronic disease processes can be activated by immunological and nonimmunological stimuli to generate leukotrienes. It appears that on activation of the cells 5-lipoxygenase is released into the supernatant and thus may exert a potent role with regard to interdependent cellular interactions. The release of leukotriene-metabolizing enzymes (e.g., <i>γ</i>-glutamyl-transpeptidase, dipeptidase) is stimulus-dependent. Polymorphonuclear granulocytes alter their release profile once the cells have been prestimulated. Thus, a precise knowledge on the leukotriene-inducing and -metabolizing enzymes is of utmost importance for future immunopharmacological interventions. It appears that the enzyme activity reflects the state of cellular activation.