A method is described for measuring polymorphonuclear leukocyte (PMN) concentrations in expelled nasal mucus. Nasal mucus specimens (0.05-0.15 ml) were diluted 1:60 in Hank's balanced salt solution. Diluted mucus was vigorously agitated to disperse contained cells, and cells were counted in a hemocytometer. The mean PMN counts in nasal mucus from healthy young adults was 7.1 X 10(6) PMNs/ml mucus, but large daily fluctuations were observed in PMN counts in the same individual. This method may be useful to investigate inflammatory conditions of the nasal cavity.