Sex hormone-binding globulin (SHBG), a homodimeric 90,000 to 100,000 molecular weight glycoprotein, is synthesized in the liver. Metabolic clearance of SHBG is biphasic, with a fast initial distribution from vascular compartment into extracellular space (half-life of a few hours), followed by a slower degradation phase (half-life of several days). Testosterone, dihydrotestosterone and estrogens circulate in serum bound to SHBG . SHBG concentrations are increased in pregnancy, hyperthyroidism, cirrhosis, oral estrogen administration and by certain drugs. Concentrations are decreased by testosterone, hypothyroidism, Cushings syndrome, acromegaly and obesity.