The clinical course of 280 patients with perennial nasal allergy was followed in a controlled study in which one half of the patients received "low zone hyposensitization (Kozaki)" while the other half received conventional hyposensitization. "Low zone hyposensitization" started with house dust extract diluted at ten thousandfold of the threshold to which patient reacted with slight redness in intracutaneus skin test. Treatment was begun with 0.02ml of the antigen extract. The dose was increased by 50per cent weekly until the patient's symptom were ameliorated. This maintenance dose was then given every two weeks." Low zone hyposensitization" group were assessed by improvement ranging 79±8per cent for sneezing, 71±8per cent for watery discharge, 58±9per cent for obstruction. The effect of "low zone hyposensitization" was equivalent to that of conventional hyposensitlzation(X2-test, P>0.25), though the relief of symptoms could be obtained earlier by "low zone hyposensitization" than conventional hyposensitization. No side-effects were observed with "low zone hyposensitization" Although the mechanism underlying the benefical effect of "low zone hypasensitization" are not yet completely understood, the authors support idiotype network theory suggesting that the reduction in symptom are due to slight decrease in the specific IgE antibody and to slight increase in the antiidiotypic antibody which is not able to react the antigen in the serum of patients. The authors claim that cell-bound antiidiotypic antibody competes chemically for the Fc receptors with the cell-bound specific IgE antibody, thereby reducing effective bridge with the antigen that can release chemical mediators for the mast cells and basophils.