Plasti-Pore (high density polyethylene) and Proplast (polytetrafluoroethylenecarbon fiber composite) are porous materials that have been employed for the fabrication of ossicular replacement prostheses. Despite many years of clinical experience with these otologic implants, questions remain regarding the tissue response elicited by these materials in the middle ear. The objective of this study was to evaluate histologically the tissue response to Plasti-Pore and Proplast implants in the middle ears of cats through one year of implantation.Plasti-Pore and Proplast total ossicular replacement prostheses, trimmed to “T” shapes, were inserted in fourteen cats, replacing the superstructure of the stapes. One Plasti-Pore and one Proplast implant were implanted in each animal. Cats were killed after two weeks, one, three, and six months, and one year.The histologic response to the Plasti-Pore and Proplast implants was similar. A fibrous capsule contained within a flattened epithelial cell sheath enveloped both types of implants. The mucosa enveloping the devices was continuous with the lining of the tympanic cavity and served to stabilize the implants. Fibrous tissue from the capsule infiltrated larger surface pores. Multinucleated giant cells and macrophages were the predominant cell types in the porosity of both types of implants. The relatively small pores of the devices did not appear to be able to accommodate both the phagocytic cells, which were responding to the particulate features of the materials, and fibrous tissue.