Forty-six patients with perennial allergic rhinitis had been treated with ketotifen(zaditen^®) for 4 weeks. Most allergic symptoms such as sneezing, nasal blowing, anosmia and nasal itching were improved significantly, but nasal obstruction was improved insignificantly. Physical findings such as color of the turbinate and rhinorrhea character were improved significantly, but turbinate swelling and rhinorrhea amound were improved insignificantly. Two cases of side effects such as drowsiness or gastrointestinal disturbance occurred, but they were only transient. It was suggested that ketotifen might be an effective drug for management of perennial allergic rhinitis with relatively mild side effects.