In enzymology, erythrose-4-phosphate dehydrogenase () is an enzyme that catalyzes the chemical reaction
The three substrates of this enzyme are D-erythrose 4-phosphate, oxidised nicotinamide adenine dinucleotide (NAD<sup>+</sup>), and water. Its products are 4-phospho-D-erythronic acid, reduced NADH, and a proton.
This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is D-erythrose 4-phosphate:NAD+ oxidoreductase. Other names in common use include erythrose 4-phosphate dehydrogenase, E4PDH, GapB, Epd dehydrogenase, and E4P dehydrogenase. This enzyme participates in vitamin B<sub>6</sub> metabolism (see DXP-dependent biosynthesis of pyridoxal phosphate).