Histochemistry of Kupffer cells for the presence of peroxidase activity at 30 minutes after injection of vesicles. Cells were isolated as described in “Materials and methods.” Cytospins were fixed in acetone and stained with 3,3′-diaminobenzidine. The large quantities of stainable material in the Kupffer cells indicate the presence of hemoglobin. The endothelial cells (E) are slightly stained indicating the presence of endogenous peroxidase. Original objective magnification × 100. The procedure was repeated 2 times with very similar results.