An HPLC procedure is described for the separation and identification of some hydrosoluble by-products resulting from the hydrolytic degradation of poly(a-hydroxyacid)s having biomedical interest: poly(DL-lactide), poly(α-lactide), poly(glycolide) and poly(lactide-co-glycolide). Peak identification was performed by comparing the respective retention times with those of pure standards. It was observed that optimum shape and separation of peaks are considerably affected by the composition of the mobile phase, consisting of acetonitrile (A) and a 0.006 M K2HPO4buffer (B), and, in particular, its pH and A:B ratio, which had to be adjusted to around 5.8 and 75:25 (v/v), respectively. Under the investigated experimental conditions (aqueous suspension, 100°C for 12 h under stirring), poly(L-lactide) is quite stable, poly(glycolide) degrades easily to glycolic acid, whereas poly(α-lactide) and poly(DL-lactide-co-glycolide) exhibit intermediate behaviour. Upon hydrolytic decomposition, these poly(α-hydroxyacid)s yield not only the corresponding acids, but also their linear dimers and, possibly, trimers, tetramers and higher oligomers.