In 25 house dust mite-sensitive patients with perennial allergic rhinitis, an analysis of platelet aggregation tests (dual-channel aggregometer, Chronolog Corp, 345 model) induced by adenosine diphosphate (ADP) was carried out. The levels of total serum IgE specific antibodies against Dermatophagoides pteronyssinus and the soluble form of the low affinity IgE receptor (sFc epsilon RII/sCD23) were estimated as well. The study was carried out in a dynamic state, before and after 2 years of treatment with specific immunotherapy. We observed a significantly diminished platelet aggregation response, which partially improved after treatment. The results of this study suggest that platelet hyporesponsiveness might be involved in the pathogenesis of house dust mite hypersensitivity.