Glucose 6-phosphatase activity was studied histochemically in the oval cells of rat livers during the early stage of hepatocarcinogenesis induced by 3'-methyl-4-dimethylamino azobenzene. Short-period perfusion fixation of the liver preserved both the ultrastructure of the liver cells and glucose

considered the possibility of the transformation of the oval cells into hepatocytes (5, 16, 21, 31), but many others were not in agreement as to the existence of such transformation and rather considered the cells to disappear by cell death and removal (9, 22, 23, 25, 26). Inaoka (1 1), in our laboratory, examining the early stage of azo dye hepatocarcinogenesis in rats, concluded that the oval cells were able to transform into hepatocytes through various transitional stages. This is one of the series of studies (2, 12) to reevaluate this conclusion, investigating the oval cells during azo dye carcinogenesis with application of the electron microscopic histochemical method for examining glucose 6-phosphatase activity which was known to be demonstrable in hepatocytes in normal livers (1).