There is currently considerable interest in the wear debris and osteolytic potential of different types of bearings used in total joint replacements. The aim of this study was first to characterize the wear and wear particles generated from two different grades of UHMWPE acetabular cups with different levels of crosslinking in a hip joint simulator. Secondly, the results for the polyethylenes were compared to an alumina ceramic-on-ceramic hip prosthesis. The wear rates of the two noncrosslinked material types were very similar at 49±8 mm³ per million cycles for the GUR 1020 and 45.6±1.4 mm³ per million cycles for the GUR 1050. Moderate crosslinking (4 MRad) significantly (P<0.05) reduced the wear rate of the GUR 1020 material by 30 % to 35±9 mm3 per million cycles. High levels of crosslinking of GUR 1050 (10 MRad) produced a highly significant (P<0.01) 80 % reduction in wear volume. Although reduced wear volumes were observed with moderate levels of crosslinking for the 4 MRad GUR 1020 material, little benefit was conveyed by crosslinking, in terms of predicted overall biocompatibility and estimated osteolytic potential. Introducing high levels of crosslinking (10 MRad) into the GUR 1050 material reduced wear and osteolytic potential by up to five-fold compared to the other GUR 1050 materials. However, compared to the noncrosslinked and moderately crosslinked GUR 1020 materials, the highly crosslinked GUR 1050 UHMWPE had only a two-fold lower osteolytic potential. The alumina ceramic-on-ceramic hip prostheses produced extremely low wear rates under both standard and microseparation simulation conditions, and consequently the osteolytic potential of the alumina bearings was estimated to be >20-fold lower than the highly crosslinked polyethylene.