We studied the long-term wear behaviour of alumina-doped zirconia femoral condyles against ultra-high molecular weight polyethylene (UHMWPE) tibial inserts. The simulator kinematics included 20 degrees of flexion/extension, ± 5 degrees of internal/external rotation, and 6 mm of anterior/posterior translation. All knee components were subjected to 10 million cycles of normal walking (2.6 KN max, freq. 1.8 Hz). Lubricant was 50% alpha-calf serum (20 mg/ml protein) with EDTA. The tibial inserts were from one lot of ram-extruded UHMWPE and sterilized with 3.5-Mrad or 7-Mrad radiation dose. Soak controls were stored unloaded in deionised water for 60 days prior to testing. Implants were studied with high-resolution confocal Raman spectroscopy after 10-Mc duration. The wear of control knees (CoCr/3.5-Mrad) averaged 4.5mm3/Mc while the wear with the ZrO2/7-Mrad combination was unmeasurably low even after 10 million cycle duration. Raman Spectroscopy at 10-Mc duration showed only the presence of the desired tetragonal phase. Thus, the ZrO2/7-Mrad bearing combination should prove excellent for active patients who may otherwise risk high wear rates over many years of use.