For patients with a totally empty middle ear a total alloplastic middle ear prosthesis (TAM) has been developed consisting of a macroporous hydroxyapatite canal-wall segment as a foundation system from which a dense hydroxyapatite ossicular chain is suspended. To connect the ossicular chain, we developed an alloplastic tympanic membrane made from a polymer.Light microscopy, morphometry, and autoradiography as well as various electron microscopy techniques were used in this study to evaluate the biocompatibility of Polyactive(R), a polyether polyester copolymer, after implantation in the rat middle ear.After between 2 and 4 weeks, implants were completely covered by tympanic-membrane epidermis and epithelium. Polyactive provoked a mild foreign-body reaction, showed a degradation rate of 54 percent after 1 year, and was nontoxic. Growth of fibrous tissue and bone into Polyactive copolymer indicated appropriate implant fixation by mechanical interlocking. The fixation of Polyactive by ingrowth of bone is promising, not only in terms of the amount of bone but also in terms of the bone/polymer interface. The latter is indicative of bonding osteogenesis in a way similar to that reported for hydroxyapatite implants.The results of this study showed that Polyactive copolymer is suitable as a degradable alloplastic tympanic membrane, both as a temporary scaffolding for the repair of tympanic membrane perforations and as a tympanic membrane in the TAM.