The antiasthmatic profile of KAA-276 (1-[1-(4-fluorophenylmethyl)-1H-benzimidazole-2-yl]-5-[2-[4-(2- carboxethyl) phenyl]ethyl]-1,5-diazacyclooctane sulfate, CAS 167264-26-8), a newly synthesized histamine H1 receptor antagonist, given by inhalation as an aerosol was investigated and compared with the profiles obtained using other routes of administration. When given by inhalation, or by intravenous or oral routes, KAA-276 inhibited antigen-induced bronchoconstriction in rats with ID50 (a dose to inhibit the antigen-induced response by 50%) values of 0.054%, 1 mg/kg, and 51.2 mg/kg, respectively. KAA-276 prevented the histamine-induced wheal reaction in rats dose-dependently with ID50 values of 0.22% by inhalation, 0.18 mg/kg by the intravenous route, and 2.3 mg/kg by the oral route. To judge from these results, inhaled KAA-276, unlike intravenous or oral KAA-276, had no inhibitory effect on the histamine-induced wheal reaction at a dose (0.054%) that is effective against the antigen-induced airway asthmatic response. Inhaled KAA-276 suppressed antigen-induced bronchoconstriction in actively sensitized guinea pigs, and histamine-induced bronchoconstriction in monkeys. These results suggest that inhalation of KAA-276 would benefit patients with bronchial asthma without inducing unwanted systemic effects.