The effect of a newly synthesized leukotriene antagonist, (E)-2,2-diethyl-3′-2-2-(4-isopropyl) thiazolyl ethenyl succinanilic acid (MCI-826), on liver injury and nephritis in mice was studied. In order to confirm the anti-leukotriene activity of MCI-826, the effect of MCI-826 on leukotriene C 4(LTC 4)- and leukotriene D 4(LTD 4)-induced vasculitis, liver and kidney injury was studied. MCI-826 was found to clearly inhibit LTC 4- and LTD 4-induced vasculitis, as well as liver and kidney injury. In addition to LT-induced reactions, MCI-826 inhibited liver injury induced by injection of either an anti-basic liver protein antibody into DBA/2 mice that had been previously immunized with rabbit IgG or of a bacterial lipopolysaccharide (LPS) into Corynebacterium parvum pretreated DDY mice. Moreover, MCI-826 inhibited nephritis, caused by injecting antiglomerular basement membrane antibody into C57BL/6 mice. These results suggest that MCI-826 can be applied to the treatment of certain tissue inflammatory diseases.