Clinical characterization of patients with allergy to Chamaecyparis obtusa (Cypress) pollen and their specific IgE antibody was investigated by using AlaSTAT assay, a new method for measurement of antigen-specific IgE antibody. Positive rate of antigen-specific antibody in patients with allergic pollinosis was 83.5% for Japanese cedar pollen and 80.0% for Chamaecyparis obtusa pollen. 76.4% of patients were sensitized both to Japanese cedar and Chamaecyparis obtusa pollen, however, 7.9% were sensitized only to the latter. As for clinical symptoms, duration of attack was short and severity was mild or moderate in the patients sensitized only to Chamaecyparis obtusa pollen. Patients who visited hospital in April, in that Chamaecyparis obtusa pollen disseminated in the air predominantly, showed significant elevation in AlaSTAT scores compared with patients who visited in February and March (p < 0.05).