We investigated whether exine-free pollen allergen particles exist together with the intact pollen grains of Japanese cedar (Cryptomeria japonica) in the air during the pollen season in Yamagata City. First, we separated the allergen particles in an Andersen multi-stage air-sampler according to their aerodynamic diameters. The amount of major allergen (Cry j I) on each stage of the sampler was determined by a sensitive fluorometric sandwich ELISA, and the pollen count of the same samples was done by light microscopy after Carberla staining. Cry j I was found in stages 1 to 6, whereas most of intact and ru|3tured pollen grains were microscopically observed only in stages 1 and 2. Second, we suctioned the air through a tandem membrane filter system (the first filter, Nuclepore filter with 5 um-pores; and the second, Millipore filter with 0.3 μm-pores). None of the pollen grains was detectable on the 0.3 μm-pore filter with light microscopy. However, Cry j I was detectable in the aqueous extract from the second filter. From these results, we concluded that pollen-free Cry j I existed in the air of Yamagata City during the pollen season.