With the introduction of the Wells Air Centrifuge,1 a renewed interest has developed in the bacteriologic examination of air, particularly in reference to its streptococcic content under various environmental conditions. The studies, including some on schools, theaters, subways, railway cars, textile factories and hospitals, have been conducted largely in New York, Boston and Iowa City.2 Our investigations, carried out in a department store3 which is the largest and perhaps at times the most crowded in the world, constitute an attempt to correlate the density of crowds with the degree of bacterial pollution of the air, in relation not only to total bacterial counts but especially to the numbers of streptococci of nasopharyngeal origin, to determine seasonal variations in respect to such data and to plot the prevalence rate for disabling colds among the employees in relation to the numbers of streptococci in the air during the course