Beta-2-microglobulin normally passes through the glomerulus into the proximal tubule where much of it is reabsorbed. serum levels are therefore an index of glomerular function. When impaired, serum levels rise in inverse ratio to glomerular filtration rate. Increased amounts of beta-2-microglobulin are excreted in several renal disorders, e.g., Balkan nephropathy, heavy metal poisoning and renal tubular disease due to therapeutic agents. Serial levels of beta-2-microglobulin in serum and urine are used to evaluate transplant viability and anticipate rejection. Following a successful graft, serum levels decline toward normal. Increasing serum levels provide an early sign of rejection. Elevated levels are also noted in lymphoproliferative disorders, neoplasms (malignant and benign), inflammatory disease, and autoimmune disease such as system lupus erythematous (SLE) and Sjogren’s disease.