Poly(epsilon-caprolactone), PCL, is a commercial biodegradable and biocompatible polyester that can be bioassimilated by outdoor microorganisms. For biomedical and environmental applications, monitoring the fate of degradation products in vivo or under environmental conditions is one of the critical steps to evaluate degradation characteristics. [H-3] radiolabeling is the best method to monitor the fate of degradable polymer chains in contact with complex living systems and to show bioassimilation. Therefore, tritiated PCL was synthesized by chemical modification using anionic activation by reaction with lithium diisopropylamide. The resulting radioactive polymer was characterized and allowed to degrade at 37 degreesC under aerobic conditions in the presence of active sludge. Comparison was made with abiotic hydrolytic degradation in pH = 7.4, 0.13 M phosphate buffer at 37 degreesC. Water-soluble degradation products were assessed by measuring radioactivity in the solution phase. It was shown that biodegradation of PCL started after a few hours and proceeded up to the ultimate stage over ca. 72 days, giving tritiated water (80-90%) and biomass. Radioactivity detection appeared much more sensitive than measurement of CO2 production or consumption to monitor degradation phenomena. In particular, it showed that the onset of biodegradation occurs earlier than that reported using respirometry.