Researchers from the University of Connecticut Health Center have investigated bone formation on PEEK and Ti surfaces using a primary human osteoblast in vitro model. Unfilled or carbon fiber-reinforced (CFR) specimens were prepared from PEEK OPTIMA. As-molded and machined surfaces were investigated. The osteoblasts in this study were derived from middle-aged male and female patients. The in-vitro performance of two PEEK-based biomaterials (unfilled or carbon fiber reinforced PEEK-OPTIMA) presented to the human bone cells as either injection molded or machined, was comparable to that of Grade 1 cpTi commonly used for implants. All in-vitro parameters (adhesion, proliferation, alkaline phosphatase activity, synthesis of bone matrix proteins and mineralization) appear to be influenced by the surface finish of the material as generated using common manufacturing techniques such as polishing, injection molding or machining. However, human osteoblasts did adhere to all test materials. The presence of mineralization suggests that PEEK may lend itself to the osseointegration of implants and that further work should follow to investigate fulfilling the mechanical requirements of such an implant system.