2,5-Diaryl tetrahydrofurans, 2,5-diaryl tetrahydrothiophenes, 1,3-diaryl cyclopentanes are disclosed that reduce the chemotaxis and respiratory burst leading to the formation of damaging oxygen radicals of polymorphonuclear leukocytes during an inflammatory or immune response. The compounds exhibit this biological activity by acting as PAF receptor antagonists, by inhibiting the enzyme 5-lipoxygenase, or by exhibiting dual activity, i.e., by acting as both a PAF receptor antagonist and inhibitor of 5-lipoxygenase. Also disclosed is a method to treat disorders mediated by PAF and/or leukotrienes that includes administering an effective amount of one or more of the above-identified compounds or a pharmaceutically acceptable salt thereof, optionally in a pharmaceutically acceptable carrier, to a patient in need of such therapy.