Poly (L-lactide)-poly (oxyethylene)-poly (L-lactide) block copolymers obtained in bulk, by a ring opening mechanism, from poly(ethylene glycol)s (PEG)s and L-lactide (LA), at 120-140 degrees C, in the absence of added catalysts are described. By using PEGs with different molecular masses, 3000 and 35 000, respectively, and varying the initial molar ratio LA to PEG, two series of copolymers with different molecular masses, relative length of blocks and hydrophilicity were obtained. Physico-chemical characterization of the copolymers had been previously performed. The morphological characteristics of the copolymers were investigated by means of X-ray diffractometry, optical and scanning electron microscopy. The biological properties of the materials were determined by evaluating their cytotoxicity, cytocompatibility, hemocompatibility and degradability using different standard tests. The results obtained indicate that the block copolymers synthesized may be useful for biomedical applications, in particular as resorbable drug vehicles. The materials are brittle and their mechanical properties are not appropriate for implant devices