Age-related histological changes were studied in various organs from SD-JCL rats reared throughout their lifespan. In aged-male rats examined at 5 to 36 months of age were frequently observed nephropathy, periarteritis, skeletal muscle degeneration, pigmentation of the follicular epithelium in the thyroid, fibrosis of the pancreatic islets, hyperplasia of the parathyroid epithelium, and changes of the acini in the extraorbital lacrymal gland. In aged-female rats sinusoid dilatation of the adrenal, and atrophy of the ovary were also noted. Perilobular fat deposition of the liver, dilatation of the gastric gland and severe hemosiderosis of the spleen were observed similar frequency in the both sexes. The nephropathy and cardiovasculopathy were major factors to cause death for males, while the main cause of death for females was tumors, especially of the mammary and pituitary glands. Enlargement of the parathyroid gland, bone resorption and metastatic calcification in the solf tissues were found in rats with severe nephropathy.