A study was undertaken in 60 adult rabbits in order to determine the effects of ossein-hydroxyapatite compound on bone healing. Standardized bony defects were produced in the distal femoral epiphyses, after which animals were randomized into four equal groups. An untreated group served as a control. One group received ossein-hydroxyapatite compound, 830 mg per day, a second group received bone mineral (ossein-hydroxyapatite compound reduced to ash, to remove organic constituents), 510 mg per day, and a third group received calcium carbonate, 650 mg per day. A series of fluorescent vital markers was administered to the animals from the 7th to the 32nd day after production of the defect. A third of the animals in each group were sacrificed 35, 56 and 84 days, respectively, after induction of the defect. Histological sections of the region of the bone defect were examined with a fluorescence microscope and resulting photomicrographs were scored with respect to degree of fluorescence, nature and degree of defect filling and structure of the newly formed bone. All three active treatment groups resulted in significantly improved mineralization as compared with the untreated control group. Treatment with ossein-hydroxyapatite compound, but not the other two active treatments, resulted in significant improvements in the pattern and quality of bone healing, particularly when assessed at 56 or 84 days after induction of the bone defect. These results indicate that ossein-hydroxyapatite compound has a beneficial effect on the process of bone healing but that this effect is lost if the organic components of the compound are destroyed or if pure calcium carbonate treatment is substituted. This strongly suggests that organic components of ossein-hydroxyapatite compound have osteogenic effects, enhancing the utilization of the mineral intake, and is consistent with previous experimental findings. It is suggested, therefore, that ossein-hydroxyapatite compound has considerable clinical potential and should be regarded as having specific, sophisticated effects on bone metabolism, rather than as a simple dietary mineral supplement.