The amount of pollen particles intruded into dwellings were determined in laboratory and fields by optical microscope counting and quantitative determination of the cedar allergen. Collections were made by gravitational settlement for number counting and 8 stage-type Andersen samplers for allergen determination to obtain the concentration and the particle size distribution. 4 levels of ventilation rate were used to characterize the intrusion rate caused by the infiltration. Settlement in indoor space is small in quantity and the concentration of airborne particles, especially of small size, were higher. A comparison of the actual measurements and the theoretical prediction of the gravitational settlement which had been developed by us were made to prove valid.