The aerodynamic diameter of biological particles determines their ability to penetrate the human respiratory system.To assess the content of allergens less than 10 pm in diameter in the particle fraction of airborne dust in order to improve control of exposure to harmful soybean aeroallergens.In this study, 98 pairs of particulate matter measuring less than 10 microm in diameter (PM10) and total suspended particulate (TSP) filters were collected in parallel and analyzed for soy aeroallergens by the inhibition enzyme-linked immunosorbent assay.The median levels found were 6 and 22.5 U/m3 for PM10 and TSP filters, respectively. A good correlation was found between soy aeroallergen content in PM10 and TSP filters. The median proportion of soy aeroallergen content in PM10 filters versusTSP filters was 28.6%, and varied widely across different days.Due to this wide variation between days, it seems that soy aeroallergen content in TSP filters is not a good surrogate of soy allergen content in PM10 filters. Further clinical studies should be conducted to assess differences in the health impact of soy allergen content in PM10 filters and TSP filters.