We are developing a new spinal implant system (SIS) without fusion (bone graft). This SIS is made from two materials, metal and polyetheretherketone (PEEK) polymer. The Food and Drug Administration recommended testing in vivo, in an animal model, whether the PEEK polymer could be used in a SIS without any harm of wear debris to the nervous tissue (spinal cord and nerve roots). The objective was to evaluate the biological response of the spinal cord and nerve roots (dura mater) to PEEK polymer particles. Twenty-four female New Zealand white rabbits were used. The rabbits were divided into three groups: test (n = 12), control (n = 9), and sham (n = 3). During the surgery, the test group received the PEEK particle injections (5 x 10(7) particles per site, lumbar and thoracic), while the control group received only the vehicle (0.9% saline solution). The sham group had the same surgical approach without injection. In each group, the rabbits were euthanized at 1, 4, and 12 weeks postsurgery. The macroscopic and semiquantitative histologic analyses of the spinal cords (dura mater) showed normal vascularization and particle adherence to the connective tissue especially at the injection sites. Neither necrosis nor swelling of the dura mater and nerve roots was observed. The PEEK polymer is harmless to the spinal cord; thus it might be used as component in the spinal implant system. Copyright 2002 Wiley Periodicals, Inc.