[en] Neutron activation analysis and use of radioactive tracers, completed by X-rays diffraction, allowed us to quantitatively study the transformations in a biomaterial (coral) implanted 'in vivo'. Before its implantation, the biomaterial is sterilized. Sterilization by thermal effect or irradiation does not induce any macroscopic modification of the crystal structure: the biomaterial preserves its biocompatible properties. Coral was implanted in ovine and procine thighbones. Biopsies were extracted after different implantation times (1 to 24 weeks). The analyzed samples for each biopsy are the intermediate part (initially the coral) and the cortical next to the implant. We have measured the concentrations of Ca, P, Sr and Mg by neutron activation, as a function of the time of implantation. The results show that the mineral composition of the intermediate part is greatly modified. The concentrations of Ca, P, Sr and Mg become comparable to those of a mature about 3 to 5 months after implantation, depending upon the experimentation. The X-rays diffraction analysis of the implant reveals a gradual substitution of the coral aragonite crystal structure by an apatitic structure. The radioactive marking of Ca and Sr, initially constituting coral, allowed to measure the transfers of elements in organism and to specify the mechanisms of its transformations. This study exhibits a Ca and Sr contribution from organism for the bone neoformation. After five months, the calcium of the implant is no longer the one from the biomaterial. These results, obtained by sensitive and selective nuclear methods, suggest a biomaterial resorption followed by a formation of apatite. 68 figs., 57 tabs