Immunocytochemical localization of cross-reactive antigens to Cry j 1, the major allergen of Cryptomeria japonica, in the pollen grains of Cupressus arizonica and Cupressus sempervirens, was conducted using transmission electron microscopy. Mature and activated pollen grains were fixed for immunocytochemistry using conventional and freezing protocols. Sections containing the samples were incubated with anti-Cry j 1 monoclonal antibody (mAb) (KW-S91). Cross-reactive antigens to Cry j 1 were detected in the mature pollen grains of Cupressus arizonica and Cupressus sempervirens, and abundant gold particles were seen in the orbicules and wall, and in the Golgi, nucleus, and inclusions in reserve materials. After 5 min of activation, labelling noticeably decreased. From 15 min to 48 h, the cytoplasm exhibits a new labelling pattern, with gold markers being associated with protein storage vacuoles. The decrease in cross-reactive antigens during the first 5 min of activation could be due to a rapid release of proteins recognized by Cry j 1 mAb during pollen attachment in the pollination droplet. Our results show that the content of allergenic proteins is unstable, displaying variation relative to the progress of germination in Cupressus sempervirens and Cupressus arizonica pollen grains. The ability to do so may be viewed as an adaptive strategy of Cupressaceae pollen grains to maximize their biosynthetic efficiency.