On fourteen volunteers with Japanese cedar pollinosis, nasal lavage and the determination of nasal airway resistance (NAR) were carried out periodically for twelve hours after an antigen challenge using antigen disk. The percentage of EG2 positive eosinophils, the number of activated eosinophils (EG2 positive eosinophils) and the amount of ECP in each sample of nasal lavage fluid were determined. 1. The percentage of activated eosinophils increased during the late phase compared with that before the challenge and during the early phase. The number of activated eosinophils and the amount of ECP increased during both phases, but more markedly during the late phase. 2. The number of activated eosinophils and the amount of ECP were compared between the group with late phase response and that without a marked late response. Both the number of activated eosinophils and the amount of ECP showed a tendency to increase in the positive group. 3. There was a statistically significant correlation between the percentage of increase in NAR and the number of activated eosinophils. The correlation coefficient during the late phase was considerably higher than in the early phase. From these findings, the increased number of activated eosinophils observed during the late phase response is assumed to have a significant relationship with increased NAR and also the hyperreactivity of nasal mucosa.