Carbon fibres are integrated by the organism without causing significant foreign body reaction, but even with normal tissue growth around and encasement of the individual fibres. However, integration of the fibres into the tissue is not as good when the fibres are coated with epoxy-resin. Within the course of several months, progressive rupturing of fibres occurs with implants of pure carbon fibres, but with the mechanical function, however, being taken over by the formation of a connective tissue structure resembling a ligament. Carbon fibre microparticles are absorbed either by macrophages or by foreign body giant-cells and are distributed throughout the organism via the lymphatic system. Through these animal experiments--and also by studying the fate of an implant in a human being,--the biocompatibility of carbon fibres in the form of long fibres as well as in the form of microparticles can be judged as being excellent.