Male albino rats of the Wistar strain were fed a protein deficient or protein free diet for a long period and their livers wers studied ultrastructurally and biochemically. The hepatocytes fell into principally degenerative atrophy demonstrating a marked decrease in cytoplasmic organelles. In addition to this, the great majority of the hepatocytes showed marked accumulation of lipid and glycogen in the cytoplasm, while in the nuclei the nuclear inclusions and nucleolar enlargement were observed. These inclusions seemed to be formed through the cytoplasmic invagination and were no longer detected in the recovery stage after re-alimentation with a control diet. It is considered that the existence of the nuclear inclusions reflects a metabolically rather inactive state caused by chronic protein deficiency. It was evident that the protein deficient hepatocytes showed a marked fragility of the intracytoplasmic membranes. This was indicated by the appearance of partial defect of the outer membrane of mitochondria, mitochondriolysis and by an increased availability of lysosomal enzyme in biochemical assay. In the atrophied hepatocytes the Golgi apparatus showed hypertrophy with electron dense contents and glycogen. These findings may indicate the significance of the Golgi-lysosome system as the bypass of VLDL release when excess lipid and glycogen were accumulated. After re-alimentation cytoplasmic organelles showed recovery. On the seventh day the hepatocytes showed mostly normal appearances ultrastructually
