Mainly microorganisms but only a few higher organisms are presently known to express enzymes that hydrolyze peptides containing D-amino acids. These enzymes can be involved in proceedings at the bacterial cell wall, in either assembly or modification, and thus cause resistance to glycopeptide antibiotics, or mediate resistance against beta-lactam antibiotics. In other cases the in vivo function is still unknown. New enzymes screened from nature, such as D-aminopeptidase, D-amino acid amidase, alkaline D-peptidase or D-aminoacylase, offer potential application in the production of D-amino acids, the synthesis of D-amino acid oligomers by promoting the reversed reaction under appropriate conditions, or in the held of semi-synthetic antibiotics.