A 5-lipoxygenase inhibitor (5-LPI) and a platelet-activating factor antagonist (PAF-A) were studied in dinitrofluorobenzene (DNFB)-induced allergic and croton-oil-induced irritant murine contact dermatitis. Both inhibitors, at 1 and 5% concentrations, significantly reduced the ear swelling in allergic dermatitis while irritant dermatitis was far less affected. This suggests that 5-lipoxygenase-dependent mediators and PAF are involved in allergic contact dermatitis and that these mediators play only a minor role in irritant dermatitis.