1. Two distinct forms of oxidases catalysing the oxidative deamidation of D-alpha-amino acids have been identified in human tissues: D-amino acid oxidase (DAMOX) and D-aspartate oxidase (DASOX). 2. The enzymes differ in their electrophoretic properties, tissue distribution, binding with flavine adenine denucleotide, heat stability, molecular size and possibly in subunit structure. 3. Neither enzyme exhibits genetic polymorphism in European populations, but a rare electrophoretic variant phenotype (DASOX 2-1) was identified which suggests that the DASOX locus is autosomal and independent of the DAMOX locus.