Steam sterilization is conventionally used for the sterilization of materials used in surgery and medicine. When subjected to repeated steam sterilization, oligomers of polyethylene terephthalate are produced on the surface of the polyester materials. The consequences of the production of such oligomers on the biocompatibility of the polyester material have been investigated. Growth inhibition of L929 fibroblast cells has been observed on the repeatedly sterilized materials in thein vitro cell-material contact studies.In vivo implantation of the repeatedly sterilized materials elicited a hostile tissue response comprising enhanced macrophage activity, which could have an adverse effect on the long term stability of the polyester materials.