Polyphosphazenes with hydrolytic labile substituents have potential as biodegradable materials. By proper choice of the substituents, polymers can be prepared which degrade in vivo to form harmless products. The rate of biodegradation and the nature of the degradation products can be varied by changing the chemical composition of the polymers. A series of new degradable polyphosphazene derivatives are described. The synthesis of phosphazene polymers with various amounts of ethyl 2-(O-glycyl)lactate or ethyl 2-(O-alanyl)lactate as cosubstituents is described. These polymers are prepared by reaction of poly[(dichloro)phosphazene) with the corresponding amine compound. Total halogen replacement was achieved by subsequent introduction of glycine ethyl ester cosubstituents. Introduction of these hydrolysis-sensitive side-groups along the polymer chain increases the degradability of poly[(amino acid ester]phosphazenes).