The effect of KW-4679 (Z)-11-[3-(dimethylamino) propylidene]-6,11-dihydrodibenz [b,e] oxepin-2-acetic acid hydrochloride, CAS 140462-76-6; proposed INN: olopatadine) on experimental conjunctivitis and rhinitis was studied in comparison with that of ketotifen (CAS 34580-14-8) using guinea pigs and rats, respectively. KW-4679 was effective in inhibiting the antigen- and histamine-induced conjunctivitis by both oral and topical administrations. These effects of KW-4679 were somewhat more potent than those of ketotifen. KW-4679 as well as ketotifen was more effective in inhibiting the histamine-induced conjunctivitis than that seen in antigen-induced conjunctivitis when they were given topically. KW-4679 inhibited the increased dye leakage into the nasal cavity induced not only by antigen in actively sensitized rats but also by histamine perfusion in non-sensitized rats by oral and topical administrations. Similar to ketotifen, the effect of KW-4679 on histamine-induced increase in dye leakage was almost same as that induced by antigen. The potency of KW-4679 was higher than that of ketotifen in the increased dye leakage induced by both antigen and histamine perfusion.