This chapter discusses serum albumin estimation and the A/G ratio, where albumin is the major protein of human plasma. Albumin is synthesized in the liver and comprises about sixty per-cent of the total plasma protein. About forty per-cent of albumin is present in the plasma and the remaining sixty per-cent in the interstitial compartment. One function of protein is the contribution albumin makes to the osmotic pressure of the intravascular fluid, which is responsible for maintenance of appropriate fluid distribution in the tissue. The other function of protein is to bind and transport substances like bilirubin, fatty acids and calcium in the blood. The most widely used methods for determining albumin are the dye binding procedures. The normal level of albumin in plasma is three point seven to four point nine grams per decilitre. Lowered levels of albumin are seen in malnutrition, liver disease, protein losing enteropathy and renal disease.