An appartus and technique for quantitative comparison of the aerobic bacterial flora disseminated by human subjects has been developed. Dissemination from three healthy subjects was studied weekly for 3 weeks. Viable particles recovered ranged from 100,000 for one subject during a 30-min period to 620,000 for another subject during a 10-min period. One of the three subjects showed appreciably less variation in numbers of organisms shed than did the other two subjects. When the subjects were examined on consecutive days while wearing sterilized clothing, total particles recovered were reduced and variations in recoveries from run to run were slightly lessened. Three consistent nasal carriers of S. aureus were measured for dissemination. No viable Staphylococcus aureus was recovered from two of the carriers. However, 460,000 typable S. aureus particles were recovered during a 60-min period from the third carrier.