Differential counts of smears and cytospins of full blood, dextran fractionated blood leukocytes and metrizoate/Ficoll fractionated mononuclear blood cells were compared. Frequencies of lymphocytes decreased in cytospins as compared with smears. The monocyte/ lymphocyte ratios were 0.24 in smears of full blood and 0.22, 0.31, 0.15 and 0.39 in smears and cytospins of dextran supernatant cells and metrizoate/Ficoll interface cells, respectively. Less than 5% of cells were broken in all preparations. The slide to slide variation was larger in preparations of fractionated cells than in smears of full blood. Cells were evenly distributed in mononuclear cytospins.