Two methods commonly used for collecting cells from a large volume of fluid-membrane filters (Millipore, Gelman, and Nuclepore) and cytocentrifugation-were compared for percentage of cell recovery and degree of cell preservation. Twenty samples of body cavity fluid were centrifuged, and the buffy coat of each was resuspended in a balanced electrolyte solution. The cellularity of each suspension was determined using both Coulter Counter and hemocytometer. Exact aliquots of each sample were collected on Millipore, Gelman, and Nuclepore filters and on slides by cytocentrifugation (Shandon). The resultant material was fixed in alcohol (95% ethanol), stained by the Papanicolaou method, mounted, and then evaluated with respect to the number of cells present and the diagnostically significant morphologic detail of the cells. Cell recovery was estimated by counting cells in known areas of each preparation and then ascertaining the total area. The Millipore filter technique consistently recovered the highest percentage of cells and preserved the best morphologic detail.