We histologically analyzed tissue biopsy specimens obtained from 4 cases of revised cementless ceramic knee prostheses. Particles were isolated from the specimens, and their size and composition were determined. Implants were removed for aseptic loosening at an average of 64 months. Histologically, polyethylene particles were seen in all cases. The concentration of the particles showed wide variation among cases. The concentration of the particles also showed a wide variation among different biopsy locations, suggesting that the particles were not distributed uniformly around the knee prostheses. Although we analyzed only 4 cases, our results show good correlation between radiographic evidence of geographic osteolysis and the concentration of wear particles. Multiple biopsy specimens may be necessary to characterize adequately particle migration around knee prostheses.