Sodium is widely distributed in food materials, more in animal sources than plants. Sodium ion concentration is very important in regulation of osmotic pressure of body fluids, preservation of normal irritability of muscles and the permeability of the cells. Most of the sodium is found in the extracellular fluid. Almost all the blood sodium is found in the plasma, there is very little in the red cells. In chronic cases the plasma concentration may be only slightly lower. A negative balance of sodium or potassium may cause renal failure. Changes in sodium concentration largely lead to severe diarrhea, vomiting, diabetes, acute pathological processes involving the brain, diuretics and hyponatraemia, lead to a salt deficiency and hence to low plasma sodium values which may be exaggerated if water losses are replaced without adequate salt therapy. Hyponatraemia results when the water content of the body is increased absolutely and relative to the sodium content so that the osmoiality of body fluid falls. The most common pathogenesis of hyponatraemia is mixed salt and water depletion. The present paper includes the study of serum sodium levels of 200 patients (according to age group and sex) with chronic renal failure (CRF) before and after the process of treatment and it has been compared with 50 normal healthy individuals comprising the control group.