The major fact in determining percutaneous implant success is the formation of a stable skin-implant junction. However, the characteristics an implant material must meet to secure a durable percutaneous seal are still unknown. The objective of this study, therefore, is to gain more insight into the mechanisms underlying implant-skin reactions by means of in vitro cell culture and in vivo animal experiments. For the in vitro experiments rat palatal epithelial cells were cultured on various implant materials and the possible influence of the initial surface free energy and state of cleanliness of these materials on the growth rate of cells was studied. The results of these experiments demonstrate no significant relation between these parameters and cellular growth. In the in vivo experiments, plasma-sprayed and dense hydroxyl-apatite percutaneous implants were inserted into the tibia and dorsum of guinea pigs and into the tibia and onto the cranium of rabbits. The implants were left in situ for 3 weeks to 8 months. Clinical and histological investigations were performed. The results show, that stabilization of a percutaneous implant by bony skeletal tissue is effective in the maintenance of a permanent percutaneous passage.