Quantification of the differential cell count and total number of cells recovered from the lower respiratory tract by bronchoalveolar lavage is a valuable technique for the diagnostic study of interstitial lung diseases. To examine the effect on the cell counts of different methods of processing the lavage fluid, two comparisons were performed. First, two methods of differential cell counting were compared using 28 fluids. One count was performed in a Malassez hemocytometer after incubation of the living cells with neutral red for five minutes at room temperature; large cells and some small cells that had incorporated neutral red were identified as macrophages. Another count was performed on cytocentrifuge preparations made using the Shandon Cytospin I and Cytospin II and stained by the May-Grünwald-Giemsa method. The percentage of cells identified as lymphocytes was significantly lower on the cytocentrifuge preparations than with the Malassez hemocytometer. In the second study, the differential cell counts on smears prepared by the two types of cytocentrifuge (Cytospin I and Cytospin II) were compared for 32 bronchoalveolar lavage fluids. The percentage of small cells (especially lymphocytes) was lower on preparations made with the Cytospin I than on those made with the Cytospin II, but the difference was not significant. The results indicate that (1) cytocentrifugation of bronchoalveolar lavage fluids does result in a significant loss of small cells, especially lymphocytes, and (2) this loss is not significantly lessened by the use of the Cytospin II.