1. D-Amino acid oxidase (D-AAO) oxidizes: D-Met, D-Pro, D-Phe, D-Tyr, D-Ile, D-Leu, D-Ala and D-Val. D-Ser, D-Arg, D-His, D-norleucine and D-Trp are oxidized at a low rate. D-Ornithine, cis-4-hydroxy-D-proline, D-Thr, D-Trp-methyl ester, N-acetyl-D-Ala and D-Lys are oxidized at a very low rate. 2. D-Asp, D-Glu and their derivatives, Gly and all the L-amino acids are not oxidized (or are at a rate which is undetectable). 3. Among all D-amino acids, D-Met is the most highly oxidized compound. The Km value is 1.7 mM. 4. D-Aspartate oxidase (D-Aspo) either purified from Octopus vulgaris or from beef kidney oxidizes only D-Asp, D-Glu and their following derivatives: D-Asn, D-Gln, D-Asp-dimethyl-ester and N-methyl-D-Asp. 5. However, D-Pro, D-Leu, D-Ala and D-Met, are also oxidized by this enzyme, but at a very low rate (between 0.2 and 0.6% of D-Asp). 6. All other D-amino acids, glycine and all the L-amino acids are not oxidized. 7. Under experimental conditions, 1 U of D-AAO is able to totally oxidize 0.2 micromol of the following amino acids: D-Met, D-Pro, D-Phe, D-Thy, D-Ile, D-Leu, D-Ala, D-Val, D-Ser and D-Arg. 8. Similarly, 1 U of D-AspO in 1 hr of incubation totally oxidizes 0.1 micromol of D-Asp, D-Glu, D-Asn and D-Gln.