We investigated the effect of IPD-1151T (Suplatast Tosilate, (+/-)-[2-[4-(3-ethoxy-2-hydroxypropoxy) phenyl-carbamoyl]-ethyl] dimethylsulfonium p-toluenesulfonate) against allergic bronchoconstriction induced by allergen and methacholine (MCh).BALB/c mice were sensitized by intraperitoneal injection of 0.5 microgram of keyhold limpet hemocyanin mixed with Al(OH)3. IPD-1151T was administered orally once a day for 5 or 14 days in doses of 10, 30 or 100 mg/kg body weight. Bronchoconstriction was measured 24 hrs after the final drug administration. IPD-1151T inhibited both antigen-mediated allergic bronchoconstriction and induction of bronchial hyperresponsiveness after sensitization or allergen challenge in actively sensitized mice. The degree of inhibition was proportional to the dose and frequency of oral administration of the agent.