The reverse action of hydrolases provides an attractive alternative to the chemical synthesis of peptides, oligosaccharides and oligonucleotides. Freezing the reaction mixture has proved to suppress competitive reactions in enzyme-catalysed peptide synthesis. After a short discussion of the influence of freezing on enzyme-catalysed reactions the current manuscript gives an overview of protease-catalysed peptide synthesis and the possible reasons of the yield-enhancing effect of freezing. The application of glycosidases and ribonucleases for synthetic purposes in frozen reaction mixtures is summarized.