Polylactide and its copolymers are produced by ring-opening polymerization of cyclic monomers. The monomers are synthesized by thermal induced unzipping reactions of oligomers. A large variety of processes can be used to polymerize these monomers. The use as starting materials in the medical industry requires a high purity of all compounds and advanced quality systems. Regulatory aspects such as cGMP and Drug or Device Master Files have to be taken into account when producing polylactides for medical applications. (C) 1998 Elsevier Science Limited. All rights reserved.