Even though there are some functional similarities between the aged kidney and the chronically damaged one, such as the reduction in glomerular filtration rate and in the sodium-water reabsorption capability, there are many physiological differences between these two groups, as is the case of erythropoietin, urea, potassium, calcium, phosphorus and magnesium renal handling. Thus, the data presented demonstrate that renal aging and chronic kidney disease constitute different clinical scenes.