GFAP is a 40-53 kDa monomeric molecule found only in adult glial cells of the central nervous system (CNS) and represents the major part of the cytoskeleton of astrocytes. Traumatic injury to the adult CNS results in a rapid inflammatory response by the resident astrocytes, characterized mainly by hypertrophy, proliferation (of astrocytes), and increased GFAP expression, resulting in astrogliosis. Thus, GFAP is considered to be a reliable cell-specific biomarker for monitoring neuronal activity under developmental and pathological conditions, such as brain injury, and retinal stress. The GFAP (human) EIA is based on a double-antibody sandwich technique and can be used to measure GFAP in human samples such as serum, plasma, culture supernatant, and cerebrospinal fluid.