A process for preparing C-terminally amidated peptides, Peptide-NH.sub.2, is presented. In a first step, a substrate component is reacted with a nucleophile component in the presence of trypsin or a carboxypeptidase using as nucleophile a compound NH.sub.2 -R to form a first reaction product Peptide-NH-R. In a second step, the first reaction product is non-enzymatically chemically cleaved to form the C-terminally amidated product, Peptide-NH.sub.2. The substrate component is selected from a) peptide derivatives Peptide-X-Y, where X is an amino acid or peptide residue and Y is OH, OMe or C-terminal modification and c) C-terminally esterified peptides, Peptide-OR', where R' is alkyl, aryl, heteroaryl, or aralkyl. The nucleophile component is selected from ##STR1## wherein A-F and A'-E' are carbon atoms or up to two hetero atoms, Y is H, alkyl, aryl, aralkyl, oxo or carboxy, X.sup.1 -X.sup.5 are H or various substituents. The cleavage may be induced by photolysis, solvolysis, reduction, rearrangement elimination, or oxidation. The process may be adapted to enzymatic synthesis and lends itself to C-terminal amidation of many types of peptides.