In an experimental study, commonly used ventilation fine filters were tested regarding their efficiency in collecting airborne particles and grass pollen allergens from outdoor air. Grass pollen allergen and particle number concentrations were measured before and after the filters, enabling collection efficiency calculations. Simultaneously, the size distribution of grass pollen allergens was measured in outdoor air using a cascade impactor. The study confirms previous indications that pollen allergens occur in the outdoor air as particles much smaller than pollen grains, and can penetrate ventilation filters to a larger extent than might be expected. The initially high collection efficiency of synthetic, electrostatically charged filters declined significantly with time of use (dust load), whereas glass fiber filters showed steady performance. A slight tendency for pollen allergenic matter to penetrate ventilation filters more than other airborne particles was noted, but no difference in the response to electrostatic charge of filters could be seen.