Sequential polydepsipeptides have been obtained by linear condensation of depsipeptide p-nitrophenyl ester active monomers. One of the products, poly-L-prolyl-L-alanylglycollic acid, is a depsipeptide analogue of a known polypeptide model for collagen. Synthesis of the active monomers involved the use of the pentamethylbenzyl carboxyl- protecting group, and the formation of depsipeptide ester bonds by accelerated active ester coupling.