In treating perennial allergic rhinitis sensitive to house-dust (HD)-mite (Dermatophagoides farinae), rush immunotherapy with HD antigen and classical immunotherapy were applied to 2 different patient groups, and the results obtained were compared. The results were as follows. 1. There was no significant difference in clinical efficacy between both groups. 2. The titer of the anti-mite IgE antibody was not changed in both groups during the course of treatment. 3. The titer of the anti-mite IgG4 antibody was increased in both groups during the course of treatment. In rush immunotherapy, the increase began within 3 months after the initiation of treatment, whereas about 6 months after the initiation in classical immunotherapy. 4. In rush immunotherapy, a smaller dose amount of antigen could increase the titer of the anti-mite IgG4 antibody. 5. It was not clear whether the increased anti-mite IgG4 antibody titer exerted clinical effects on allergic symptoms. Patients with perennial allergic rhinitis may receive benefit from rush immunotherapy. The antigen-specific IgG4 antibody seems to be an index in evaluating immunotherapy objectively.