Antigens of the mouse H-2 locus were studied on isolated liver cells by immunoferritin labeling. Cell suspensions were obtained by gentle homogenization of mouse livers that had been perfused with hypertonic sucrose to loosen cell junctions. Hepatocytes showed sparse labeling of H-2 antigens on the order of 1% of that present on peritoneal monocytes. The slight hepatocyte labeling appeared to be specific for the H-2 locus, since there was essentially no label on congenic control hepatocytes. Other cells in the liver cell preparations were more heavily labeled. Bile duct epithelial cells showed heavy labeling on their lateral surface membranes, but none on their apical brush borders. The preparations contained another nonparen-chymal cell type that was densely labeled, but it was not positively identified. Spleen lymphocytes added to liver homogenates and carried through the cell isolation procedure with liver cells showed typically heavy ferritin labeling. These observations suggest that the expression of histocompatibility antigens by tissue cells is likely to be quite variable.