Low molecular-weight polylactic acid (PLA) was obtained by direct polycondensation of a mixture of 95% L and 5% D-lactic acid isomers, without catalyst, at 195 degrees C. This polymer was used for the synthesis of microspheres by emulsion-solvent evaporation method. Gel Permeation Chromatography (GPC), X-ray Scattering (XRD), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) techniques were applied to follow morphological and structural changes of particles along in vitro degradation at 37 degrees C. The original microspheres were amorphous but could crystallize partially upon heating. Samples stored in a humid environment exhibited an increase in the crystallization capability upon heating. Initial smooth-surface microspheres were transformed to porous particles at the time of degradation at pH = 7 (37 degrees C). The shape of mass loss vs, time curve supports the presence of a heterogeneous bulk degradation process. After hydrolytic degradation the residual particles showed a molecular weight decrease and a crystallinity increase. After 90 days the crystallinity attained a value of 53%. The X-ray diffraction spectrum indicated the formation of a crystalline oligomeric structure. Crystallization of low molecular weight species will not enable the desired PLA absorption in drug delivery systems.