Numerous investigations proved the impressive suitability of alpha-tocopherol as a stabilizer for ultra-high molecular weight polyethylene (UHMW-PE) used for endoprostheses. Regarding the biocompatibility of this new biomaterial, in-vitro celltoxicity tests gave no hint for a cyto- or genotoxic activity. In this study, animal experiments are carried out to further ensure the biocompatibility of this biomaterial. Thin UHMW-PE-films (20 x 6 x 0.23 mm3) were implanted subcutaneously into rats. Morphology and reactivity of surrounding connective tissue against either pure UHMW-PE material or UHMW-PE containing alpha-tocopherol were studied at timed intervals (2 weeks, 3 month, and 6 month after operation) in 3 groups of animals, each group comprising 10 animals. Parallel to these tests, material changes were investigated in these 3 groups of 10 animals at the same intervals after operation with the help of infrared spectroscopy (FTIR). Within the implantation time, no noteworthy oxidative degradation could be observed. The amount of lost alpha-tocopherol due to diffusion is low enough to ensure a lifetime stabilisation of the UHMW-PE. The implants were all well tolerated and definitely encapsulated already 2 weeks after operation. Presence or absence of alpha-tocopherol in the implants did not evince morphological differences. Therefore, negative consequences were not manifest in the presence of alpha-tocopherol.