We investigated the effects of S-(4-dimethylaminobenzyl)-N-[(2S)-3-mercapto-2-methylpropionyl]-l-cysteine (SA6541), a potent leukotriene A 4 hydrolase inhibitor, on early phase of carrageenan-induced dermatitis model. Carrageenan injection induced edema and neutrophil influx in the mouse ear. SA6541 inhibited edema formation and neutrophil influx. SA6541 also inhibited leukotriene B 4 production but not prostaglandin E 2 production in the mouse ear. On the other hand, indomethacin inhibited edema formation but not neutrophil influx. Indomethacin also inhibited prostaglandin E 2 production but not leukotriene B 4 production. Combination therapy with SA6541 and indomethacin strongly inhibited edema formation in comparison with treatment with either agent alone. These results suggest that leukotriene B 4 may be important in the pathogenesis of dermatitis.