To quantitatively analyze cellular elements in mucopurulent nasal secretions from patients with chronic paranasal sinusitis, we studied five mucus-liquefying agents--dithiothreitol (DTT), ethylenediaminetetraacetic acid tetrasodium salt, propylene glycol, serratio peptidase and urea--with Hanks' balanced salt solution used as a control. Agents were compared for the number of cells, the mucus-liquefying effect and the staining characteristic of cells in cytocentrifuge-prepared smears. The results indicated that the treatment of nasal secretions with 10 mM DTT provides more clear and detailed cytological preparations for quantitative cytology of nasal secretions.