Implanted bovine apatite is highly osteoconductive, since it serves the host tissue as a "guide-line" for the deposition of newly developing bone tissue. It is well tolerated, but it showed no signs of being resorbed during the course of the experiment. Previous impregnation of the bovine hydroxyapatite with a low molecular humate substance obviously encourages its resorption. This is most easily explained by the known ability of humate to induce the activation of leucocytes. The occasional over-resorption of the apatite is dependent (1) upon the preparation of the implant (granulate) and (2) the local concentration of the humate. Future research is being directed towards the production of a satisfactorily usable form of humate and apatite and the investigation of its HIV blocking action on heterologous cancellous bone.