In the present study, we examined the relationship between the increase in respiratory resistance following exposure to antigen and the IgE level in the identical rate sensitized with DNP-As. Additionally, we investigated the effects of the antiallergic drugs, suplatast tosilate and azelastine hydrochloride, which have been reported to suppress the production of IgE, on the increase in respiratory resistance in rats following exposure to antigen. The IgE antibody level rose to its highest value on day 10 during the course of sensitization with DNP-As, and decreased sharply on day 20. The changes of IgE antibody level in the azelastine hydrochloride-administered group were similar to those in the distilled water-administered group (control). In contrast, in the suplatast tosilate-administered group, the IgE antibody levels were lower than those in the control group at days 10 and 15. The ratio of increase in the respiratory resistance induced by the early and late phase responses in the control group reached its highest value on day 15, and then decreased gradually. In contrast, in both the azelastine hydrochloride and suplatast tosilate-administered groups, the ratio of increase in the respiratory resistance induced by the early and late phase responses remained almost unchanged, and was lower than that in the control group at day 15 or 20. In the present study, an increased peak of respiratory resistance was observed at 5 days after the appearance of an increased peak in the IgE level.