Out of 56 thioacetamide (TAA)-fed rats hepatocellular carcinoma were found in four instances after 300, 360, 450 and 495 days in the present experiment. Of the four tumours, two showed lung metastasis. The size of TAA-treated hepatocyte nucleoli increased greatly after several weeks of feeding. Two enzymes, succinate dehydrogenase and glucose-6-phosphatase were found in both cytoplasma and nucleoli of hepatocytes of which nucleolar localizations are quite new. In hepatocellular carcinoma, malignant cells lost glucose-6-phosphatase activity completely in cytoplasm and nucleoli though succinate dehydrogenase activity was present in these organelles.