Chemical and structural surface changes at enosseous bioglass-ceramic-implants (Ap 40) were investigated by means of electron microprobe after an implantation period of 4 to 52 weeks. An intimate bonding between regenerated bone and bioglass-ceramic surface was evident at points already after 4 weeks. Initial degradation processes at implant surface came to a standstill after 12th week. A calcium and phosphorus rich layer of great importance for implant stability and biocompatibility was formed immediately contacting the bone. This surface layer had a thickness of nearly 25 micrometers -- 30 micrometers at 12 weeks and remains unchanged up to 52 weeks. The registered calcium and phosphorus impulse rate (cps) is equal to that of neighbouring bone. Chemical similarity of implant surface makes bioglass-ceramic Ap 40 a suitable biomaterial for durable bone replacement.