Research on cellular regeneration has been of great importance to both the experimentalist and the clinician interested in liver disease, as three of the major complications of hepatic injury in man have been attributed to abnormalities in regeneration: Its absence or relative deficiency is responsible for hepatic failure in processes which cause acute necrosis of the liver. Changes in cell arrangement and distortion of the normal lobular pattern after liver regeneration may lead to portal hypertension and its sequelae in cirrhosis. Uncontrolled regenerative hyperplasia is characteristic of hepatoma. Investigation of liver regeneration has been facilitated by development of in vivo techniques for evaluating humoral factors,1 electron microscopy,2 isolation of subcellular fractions of the liver for chemical analysis,3 and metabolic studies with the use of radioactive precursors of nuclear and cytoplasmic constituents.4 Experimental observations have been partly extended to man by analysis of serial biopy specimens obtained in subjects with liver