The gross biocompatibility of the materials implanted was generally satisfactory. Weight gain during implantation due to net sorption of fluid was negligible for PPO and UHMWPE. Delrin AF specimens gained less than 0.5%, while SP-1 and SP-21 gained up to 2% in weight. Amoco-AI specimens gained up to 7% in weight. The friction coefficient of implanted samples of UHMWPE was lower by 20 to 40% than for the virgin material. The friction coefficient of the other implanted materials was usually somewhat higher than the friction coefficient of the corresponding virgin material. The largest increase in the friction coefficient was 38% for Delrin AF. Wear characteristics of UHMWPE were not significantly changed by implantation for periods of three years. UHMWPE was the only acceptable bearing material tested. Significantly higher wear rates were observed for implanted blocks of the SP-21, a Delrin AF, and an Amoco-AI material. Because of excellent creep resistance, virgin wear rates, and other favorable properties of the polyimides, further testings are in progress to indicate potential application of these polymers.