Four different poly(organophosphazenes) bearing esters of glycolic or lactic acid as side groups have been synthesized in order to investigate their stability in aqueous media. The polymers are poly[bis-(ethyl glycolato)phosphazene],poly[bis(ethyl lactato)phosphazene],poly[bis(benzyl glycolato)phosphazene], and poly[bis(benzyl lactato)phosphazene]. The benzyl esters of glycolic and lactic acid were prepared by the base-catalyzed transesterification of their ethyl esters with benzyl alcohol at 90 degrees C. Poly(dichlorophosphazene) was treated with a large excess of the appropriate sodium acid ester at 50 degrees C to yield the fully-substituted polymer. To avoid unwanted molecular weight decline, these polymers were stored-under nitrogen or in vacuum. Hydrolytic decomposition profiles in aqueous media were monitored by P-31 NMR spectroscopy and by gel permeation chromatography (GPC). The possible utility of these polymers as biomedical materials is discussed.