Surface reactions caused by pollen, such as hay-fever, asthma and dermatitis of the exposed parts, vary in intensity at different seasons, during different weeks of the same season, or at different times during a given day. They may vary during the same day in different geographic localities; in different localities in the same city, or even in different rooms of a house. A great deal of light can be thrown on such apparently groundless variation in the intensity of symptoms through daily determination of the pollen content of the air; in fact, without such determinations a physician may find it difficult to account for the peculiar behavior of many of his patients. For this reason we report daily observations on pollen content of the air during the period of one year in two localities in Kansas City, one in the suburbs and one on the eighteenth floor of a building