Abstract: Based on recent investigations showing iatrogenic, profound neutropenia (and the fever spikes that often accompany it, which must be medicated immediately to avoid the risk of life-threatening infection) can most accurately be monitored by obtaining daily mucosal neutrophil counts from the patient's oral mucosa rather than obtaining daily counts of the patient's blood neutrophils as in the past, a mouth wash method has been developed for collecting muscosal neutrophils. The mouth wash samples so collected are delivered directly, or in aqueous dilution to a sample pad supported on a strip which sample pad has deposited thereon reagents enabling a colorimetric, fluorescent or chemiluminescent assay of the quantity of an enzyme characteristic of human neutrophils that is present in the sample. This measured quantity can be correlated to mucosal neutrophil count. The method shows outstanding sensitivity, precision and accuracy relative to microscopic methods of counting mucosal neutrophils.