An enzyme capable of reducing α-amino-adipic acid (α-AAA) to its δ-semialdehyde was found to exist in yeast extract and designated as “α-aminoadipic acid reductase”. The enzyme was purified about ten fold by ammonium sulfate fractionation and demonstrated to require ATP, TPNH and Mg++ for the reaction. A marked activation by glutathione was observed. However, no evidence of the participation of CoA and lipoate was obtained. Monoiodoacetate at a concentration of 1.2×10−3M depressed the reaction to 25 per cent of normal, and p-chloromercuribenzoate at a concentration of 2.5×10−3M completely inhibited the reaction. The Michaelis constant for DL-α-amino-adipic acid was found to be 1.06×10−35M. The enzyme activity was optimal at pH 7.6 to 8. The enzyme is specific for α-aminoadipic acid and no reaction was observed with a number of derivatives of α-aminoadipic acid including piperidine-2-carboxylic acid.