Glyceraldehyde 3-phosphate dehydrogenase (abbreviated as GAPDH or less commonly as G3PDH) is an enzyme of ~37kDa that catalyzes the sixth step of glycolysis and thus serves to break down glucose for energy and carbon molecules. In addition to this long established metabolic function, GAPDH has recently been implicated in several non-metabolic processes, including transcription activation, initiation of apoptosis, ER to Golgi vesicle shuttling, and fast axonal, or axoplasmic transport. In sperm, a testis-specific isoenzyme GAPDHS is expressed.

GAPDH is overexpressed in multiple human cancers, such as cutaneous melanoma, and its expression is positively correlated with tumor progression.[18][19] Its glycolytic and antiapoptotic functions contribute to proliferation and protection of tumor cells, promoting tumorigenesis.
GAPDH has been implicated in several neurodegenerative diseases and disorders, largely through interactions with other proteins specific to that disease or disorder. These interactions may affect not only energy metabolism but also other GAPDH functions.