Birch (Betula sp.) pollen grains are the main cause of seasonal allergies in northern and central Europe. The allergen particles released from the grains are often well distributed in the air. Due to their size, airborne protein particles can easily penetrate into the lower parts of the respiratory airways and may lead to symptoms of asthma. The purpose of this paper was to quantify both Betula sp. pollen grains and allergens in the air. Materials for the investigation were collected in the spring of 2003 with two Hirst-type pollen volumetric traps. Tapes from one trap served for routine birch pollen grain counts, while those from the second for the immunodetection of birch allergens. As birch pollen allergen concentration is seen as dark spots on X-ray films densitometric measurements of the spots were used to quantify birch-pollen antigen concentrations in the air. In most instances, birch pollen counts corresponded with birch pollen allergen levels. However, on several occasions outside the pollen season, only grains or only allergens were detected. Apart from sampling variability, this could be due to faulty/dead pollen grains or submicronic airborne allergen particles. Counting intact pollen grains and antibody-based detection of allergen molecules are efficient tools in controlled allergen avoidance.