Previous work in our laboratory had shown that serum TAU was lower in aged rats when compared to adult controls. The present study sought to determine if the age-related changes in serum TAU were reflected in tissues where TAU was known to have significant physiological relevance. TAU content was found to be significantly decreased in the atria, kidney and caudal artery of 30-month-old male Fischer 344 rats. Furthermore, glutamine content was also found to be altered by aging in both the heart and kidney. Exogenously administered glutamate was shown to increase renal glutamate content and decrease renal TAU content; however, this response was significantly attenuated in aged rats. Subcellular content and distribution of amino acids were not altered in the cerebral cortex of aged rats. Serum TAU was, however, significantly decreased in aged rats. It was concluded that renal conservation and regulation of TAU appears perturbed in the aged rat. Furthermore, the brain and heart can maintain tissue stores of TAU despite a significant age-related decrease in circulating TAU. Our data also suggests that there is an interrelationship between glutamate and TAU stores in the kidney.