Atopic dermatitis positive to Japanese cedar pollen showed the recurrence or worsening of the symptoms during the pollen season. In 22 cases, 6 children (mean, 11.4 y) and 16 adults (29.5 y) who showed positive to Japanese cedar pollen by RAST, CAST analysis were done by Cry j 1 0.01 approximately 10 micro g/ml and they showed the significant higher simulation indices compared to controls (P<0.01). Randomized analysis of the hyposensitized patients (10 cases) and non-hyposensitized (12 cases) showed significant lower stimulation indices in hyposensitized patients (P<0.01). In six cases stimulation indices were compared after one year of hyposensitization therapy. Four cases to whom hyposensitization were newly introduced showed the significant decreases of stimulation indices: 19.83+/-4.97 (mean+/-SEM) to 6.84+/-6.36 (65.0%) by Cry j 1 0.01 microg/ml, 19.73+/-5.65 to 6.85+/-1.78 (65.3%) by 0.1, 17.88+/-5.11 to 6.36+/-1.53 (64.4%) by 1, and 20.03+/-5.29 to 6.11+/-1.39 (69.5%) by 10, and they showed the significant decreases (P<0.05). By anti-IgE it decreased significantly from 35.08+/-3.42 to 7.00+/-1.77 (79.7%) (P<0.01). In two cases who got hyposensitization therapy for 2 years and 1 1/2 years each, there were no significant decreases of stimulation indices. The symptoms improved significantly and there were little or no recurrence of the symptoms. Symptom scores (Rajka & Langeland) showed significant decreases. Thus, hyposensitization by cedar pollen in atopic dermatitis is a promising treatment.