This report is based on 4 comparative experimental series is sheep using a cementfree total hip replacement model. Basically a smooth stem design was compared to a step stem design for biomechanical interlocking anchorage. Both designs were implanted as pure high density Al2O3-ceramic components and as Al2O3-ceramic parts coated with Bioglass or Bioglass-ceramic (post op. follow up 13 months, 17 animals). None of the 4 stem modifications showed a tendency for permanent stabilisation or bonding in bone. Besides insufficient bonding of the glass coatings to the substrate and apparent biodegradability of the bioglass coatings in the body, insufficient biomechanical knowledge of endosteal direct anchorage of prosthetic devices is the main reason for failure in these experiments. An exclusive biochemical way of anchoring prosthetic parts in the marrow cavity is rejected. The results presented are discussed in the light of the recent literature.