A new technique is presented to detect and quantify birch (Betula pendula)-pollen allergens directly on air-sampling filters. It is based on the use of specific antibodies, enzymatic reactions, and measurement by chemiluminescence or densitometry. The major pollen antigens are the most important birch allergens. The antibodies used recognize birch-pollen antigens which thus correspond to allergens. Calibration was done with a standardized extract of birch pollen for skin prick testing. The correlation coefficient for the logarithms of luminescence and the amount of birch-pollen allergen applied on filters was > 0.98 in the range 0.04-200 SQ units. A similar correlation was found for the logarithms of the integrated densitometry values and the amount of birch-pollen allergen applied on filters. The number of major pollen-antigen particles or grains on filters could be estimated by counting the major stained spots produced by precipitated enzymatic products. The correlation coefficient was 0.90 for the logarithms of the number of counted major antigen spots and the calculated antigen amount obtained by luminometric measurements. Our results demonstrate that birch-pollen allergens can be determined directly on air-sampling, Teflon-based filters by luminometry, optical density, or particle counting.