Tribological studies at 25°C in a 50 percent relative-humidity air atmosphere were conducted using hemispherically tipped 440C HT (high temperature) stainless steel pins sliding against ultrahigh-molecular-weight polyethylene (UHMWPE) disks. The results indicate that sliding speed, sliding distance, contact stress, and specimen geometry can markedly affect friction, UHMWPE wear, UHMWPE transfer, and the type of wear mechanisms that occur. Adhesion appears to be the predominant wear mechanism; but after long sliding distances at slow speeds, heavy ridges of transfer result which can induce fatiguelike wear on the UHMWPE disk wear track. In one instance, abrasive wear to the metallic pin was observed. This was caused by a hard particle embedded in the UHMWPE disk wear track. The origin of this particle was uncertain.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Hartford, Connecticut, October 18–20, 1983