In enzymology, a tryptophan dehydrogenase (EC 1.4.1.19) is an enzyme that catalyzes the chemical reaction

L-tryptophan + NAD(P)+ + H₂O ${\displaystyle \rightleftharpoons }$ (indol-3-yl)pyruvate + NH₃ + NAD(P)H + H⁺

The 4 substrates of this enzyme are L-tryptophan, NAD⁺, NADP⁺, and H₂O, whereas its 5 products are (indol-3-yl)pyruvate, NH₃, NADH, NADPH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-NH2 group of donors with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is L-tryptophan:NAD(P)+ oxidoreductase (deaminating). Other names in common use include NAD(P)+-L-tryptophan dehydrogenase, L-tryptophan dehydrogenase, L-Trp-dehydrogenase, and TDH. This enzyme has at least one effector, calcium.

• Vackova K, Mehta A, Kutacek M (1985). "Tryptophan aminotransferase and tryptophan dehydrogenase - activities in some cell compartments of spinach leaves - the effect of calcium-ions on tryptophan dehydrogenase". Biol. Plant. 27 (2–3): 154–158. doi:10.1007/BF02902153.