A method of studying the trapping of white blood cells on glass beads is described. The eosinophils had the greatest tendency to adhere to the glass beads, followed by the neutrophil granulocytes, while the mononuclear blood cells exhibited the least tendency to adhere. The monocytes and lymphocytes had a similar passage capacity. The basophil granulocytes appeared to pass over the glass beads without adhering. Granulocytes with rod-shaped and segmented nuclei had similar passage capacities. The storage of heparinized food had no noteworthy effect on the percentage passage capacity. The neutrophil granulocytes adhering to the glass beads became firmly attached, while the eosinophil granulocytes and the mononuclear blood cells could be more easily washed out.